One year ago it was Rafael Nadal and Serena Williams who raised the singles trophies at Roland Garros 2013. Rafa had defeated Novak Djokovic in a five-set semi-final, then comfortably beat countryman David Ferrer. It was Rafa's eighth Garros crown in nine tries. Meanwhile Serena defeated final-round opponent Maria Sharapova amid severe rocketry by both, Serena closing out matters with a barrage of first serves. After their Garros triumphs, both Rafa and Serena went on to more glory including triumphs at U.S. Open 2013. Currently the two stand #1 atop the respective men's and women's official rankings.
 
Thus Rafa and Serena are the seeming favorites to capture the men's and women's singles crowns at Garros 2014. But their margins of certainty are very different. One of them faces a host of dangerous pitfalls -- opponents seemingly able and assuredly willing to take down the front-runner. Meanwhile the other seems firmly dominant against any rival. Curiously, it is the younger of the two -- the one closest to prime tennis age -- that is in the greater jeopardy.
 
The tests will come on the historic grounds not far from downtown Paris. The setting at Stade Garros is hardly recognizable from the forested one I remember from long ago. The original central arena, built in 1928, is now a modernized Court Chatrier, seating 15,000. Meanwhile Court Lenglen, built in 1994, seats 10,000. The already splendid site is being expanded and redesigned to enhance the openness and greenery. Plans call for two retractable-roof stadia including a rebuilt Chatrier.
 
The crushed-brick and porous-limestone, "red clay" courts provide good drainage, moderately good traction, and a bounce slower than that at the other Slams, though the difference in bounce speed is less than it was long ago. Still, there will be fewer service aces than on nonclay courts and fewer very short points along with more breaks of serve. Basic tactics among the topmost players will be broadly similar to those used on hard courts, with far more emphasis on offense than on clay in earlier times. Though their rocketry will be somewhat dulled, powerful servers will intend to achieve early dominance in points, and powerful ground-strokers will enjoy more time for shot preparation. Drop shots and close-in cat-and-mouse play will be enhanced by the low bounces. Net attack will be less frequent than on other surfaces, but if the opportunity is created, finishing points at net will be a winning tactic.
 
Here are data from the late rounds at recent Slams, where the numbers reveal the slower bounce at Garros:
 
Aces and Points Won by Servers (% of total points)
Wimbledon 2006-2013, aces 10.1%, PwSv 66.8%
U.S. Open 2006-2013, 7.4%, 63.4%
Australian Open 2006-2014, 7.6%, 62.8%
Garros 2006-2013, 5.5%, 61.8%
 
RAFAEL NADAL
 
He is universally acknowledged the greatest clay-court player in tennis history, but for Rafa at age 27 and soon to turn 28, success in 2014 has been hard to earn. In January the powerful megastar reached the final at Australian Open, but he was then outplayed and defeated by an unexpected finalist, Stan Wawrinka. Two months later Rafa reached the final at Miami 2014 but then lost to Novak Djokovic. Then came quarter-final-round losses on clay to two players Rafa had habitually defeated -- Ferrer and Almagro. Next Rafa was strong at Madrid but had trouble in the final round against Japanese riser Kei Nishikori. Kei's accuracy and aggressiveness brought him the first set and a service-break edge through most of the second. Rafa was then able to step up his play, and Kei amid back pain later retired from the match. Then in Rome where for several days the players struggled amid swirling winds and clay dust, Rafa survived three-setters against Gilles Simon, Michael Youzhny, and Andy Murray, only to lose to Djokovic in a three-set final marked by stretches of magnificently aggressive tennis by Novak. It was Novak's fourth consecutive win over Rafa following Rafa's final-round victory over Novak at U.S. Open last year.
 
All these episodes -- the losses to Djokovic, the surges by Wawrinka and Nishikori, and the challenges by others to Rafa on clay, confirmed that despite Rafa's many years of dominance at Garros, serious barriers lie ahead in his current quest for a ninth Garros crown.
 
The Prime Opposition
 
The foremost protagonist, almost coequal with Rafa, is the superbly talented Serbian star, Novak Djokovic, now 27. Novak's prospects had been clouded by a damaged right wrist, which hampered Novak in a loss to Federer at Monte Carlo and sidelined him thereafter until mid-May. But on the clay at Foro Italico he advanced routinely through the early rounds and then overcame Raonic in three sets in the semis. In his remarkable final-round victory over Rafa, Novak's heavy artillery showed no concern for the recently injured wrist. Novak is at his best when receiving serve. (His game-winning percentage when receiving serve on clay is by far the highest among pros this year -- an astonishing 44%.) Novak has often done well at Garros, having reached the semis five times, the final once. He needs a Garros triumph to become the eighth in tennis history to complete the Career Grand Slam.
 
Roger Federer, 32, was Garros champion in 2009, has been runner-up four times, and last year reached at least the quarters for the ninth straight year. This year after reaching the final in Monte Carlo, Roger sat out Madrid upon wife Mirka's birth to a second set of twins. Reappearing at Rome, Roger lost his first match to Chardy amid difficult winds that made for many errors. Aside from that match in Rome, Roger has not competed since mid-April, so that although he may be rusty, he should be well rested for best-of-five-set matches at Garros.
 
Prominent among the other contenders is Stan Wawrinka, 29, the sturdy Swiss warrior, this year's champion at Australian Open and also at Monte Carlo. Stan defeated Djokovic, Berdych and Nadal in Australia, then Raonic, Ferrer, and Federer in Monte Carlo. He brings a powerful serve along with potent ground strokes, especially his backhand one-hander, which allow him to create and then exploit court dominance. His triumph on clay at Monte Carlo was achieved while losing serve only twice in 42 serving games. Stan is second to Federer in game-winning percentage in 2014 when serving on clay, at 87% vs. Roger's 89%.
 
David Ferrer, 32, has been Spain's second-best clay-courter for many years, applying a style built on determination and court-craft. He defeated Rafa at Monte Carlo this year, but before that David had lost their last 17 head-to-head clay-court matches going back to 2005. David's best result at Garros came in reaching the final in 2013, and he reached the semis in 2012. In both cases, he lost to Nadal in straight sets. David has a forcing serve and relentless ground strokes which are surprisingly potent for David's relatively small size. These weapons are backed up by a strong match temperament and fine mobility in defending. He does not accept defeat easily.
 
Rising in the rankings on all surfaces is Kei Nishikori, 24, who won Barcelona Open on clay in April. At Madrid, having just entered the world's official top-ranked ten, he was the only non-Spanish player to reach the tournament's final four, joining Ferrer, Nadal, and Bautista Agut. In a riveting semi-final, Kei showed plenty of resilience in overcoming tiredness and a troublesome lower back or hip problem to defeat Ferrer, where both men rallied relentlessly and aggressively throughout. Nishikori also defeated Ferrer earlier, in a three-setter at Miami. After Kei's high-level performance in losing to Nadal at Madrid, Kei was sidelined at Rome resting his back injury.
 
Andy Murray, 27, returning this year from back surgery in late 2013, showed in Rome that he too belongs on the list of Rafa's strong challengers. Andy commands blistering power, comfortably generated in all strokes, and is thus able to maintain severe pace in extended rallies. Against Rafa in Rome, for long stretches he was able to force Rafa to uncomfortable hitting positions, sometimes deep behind baseline. The rallies of the two in Rome were of breathtaking severity, both men driving with full power to the sides and corners relentlessly, where the slightest softness in rallying by either man usually resulted in fierce and often point-ending rockets by opponent. Murray won the first set behind near-perfection but then lost the next two behind only slight decline on his own part amid furious assault by Rafa.
 
The others currently ranked in the top twenty or so must be considered dangerous, but there are several whose improved recent results make them especially worth watching. Among these are Colombian Santiago Giraldo, who defeated Andy Murray in Madrid, the mercurial Italian Fabio Fognini, and Ernests Gulbis, whose strong play in 2014 had long been awaited. Fognini is quick, mercurial both in personal manner and in style of play.
 
Also to be watched is Grigor Dimitrov, who turned 23 soon after defeating Berdych at Rome. Grigor has the tools for success on any surface and made a strong run at Rome, reaching the semis. But there Grigor's power was contained by Rafa's defenses sufficiently for Grigor's errors to multiply. Even more powerful than Dimitrov is Canadian Milos Raonic, 23, who also reached the semis in Rome only to lose, albeit closely, to Djokovic.
 
For these prospective opponents, beating Nadal seems to require steady application of heavy power, aggressively directed, thereby neutralizing Rafa's dominance during points, meanwhile staying ready to exploiting any softness in a Rafa reply, avoiding long baseline exchanges.
 
Still out with wrist troubles is Argentine pounder Juan Martin del Potro.
 
SERENA WILLIAMS
 
Like Rafa, Serena won both Madrid and Rome in 2013, the main clay preliminaries to Garros, where she lost only one set in winning the tournament. She won U.S. Open 2013, again with loss of only one set, and she won the year-ending round-robin in Istanbul. No woman, it seemed, could answer Serena's extreme power in serving and stroking nor break down her athletic court coverage.
 
This year, Serena, now 32, lost in the fourth round at Melbourne Park, but in March she captured Miami 2014, defeating three top-tenners, all in straight sets, reestablishing herself as the sport's unofficial La Prima. She won three matches at Madrid while showing a heavily wrapped left thigh but then withdrew prior to the quarter-finals. A withdrawal at Rome the next week seemed likely, but she reappeared, capturing the tournament without thigh wrapping while losing only one set.
 
Serena's Prime Challengers
 
Serena's comfort at Garros will be enhanced by the withdrawal of Victoria Azarenka, world #2 at the end of 2013 but largely inactive since then with foot injury. Victoria had been runner-up to Serena in the final at U.S. Open, winning one of their three sets.
 
Taking Vika's place as the secondary favorite at Garros is Maria Sharapova, 27, whose success this spring recalls her fine run on clay last year when she reached the Garros final. Maria reached the semis at Miami this year, losing to Serena, and then won the clay-court crowns at both Stuttgart and Madrid. An unexpected loss to Ivanovic in her second match at Rome amid windy conditions followed. Thus Maria seems to have found a liking for clay, where the slow bounce improves her preparation time in unleashing her relentless power. Maria's screamers to the corners and sides stretch the opponent's mobility and often become outright winners or yield weak replies.
 
This year's Australian Open winner was Li Na, 32. Na had won Garros three years ago, so this was her second Slam triumph. Her strong play, now as world #2, continued in March 2014 when she reached the semis at Indian Wells and the final at Miami, losing to Serena in the latter event. At Madrid and Rome, she lost to Sharapova and Errani, respectively, in three-setters.
 
Rising Simona Halep, age 23 at height 5-6, joins our top tier of contenders. The Romanian star's climb has been remarkable -- from #47 at the end of 2012 to #11 one year later. Her present rank of #4 assured her a path to the semis at Garros without having to face Serena Williams. Simona has good power and aggressiveness to go with a varied defense-offense style -- sound in serving, stroking, movement, variety, and avoidance of error. In her final-round loss to Sharapova at Madrid, Simona won the first set but was unable to withstand Maria's stepped-up power and accuracy. At Rome, she withdrew with abdominal injury prior to her second match.
 
Serena stands as the sole member of our top tier of Garros warriors, and Sharapova, Li, and Halep compose the second, also joined by a strong clay-courter, Sara Errani. Sara's mobility, determination, and strong shot-making ability kept her close to Serena in their final in Rome. It had been a fine tournament for the Italian star, but a leg/hip injury late in the first set abruptly spoiled her hopes.
 
The third tier is much wider, including the likes of Radwanska, Kvitova, Kerber, and Jankovic. Recent risers bidding to climb into the group will be Eugenie Bouchard of Canada, Sloane Stephens of America, and Caroline Garcia of France, whose power game nearly unseated Agnieszka Radwanska at Madrid. Switzerland's Belinda Bencic, 17, schooled by the mother of Martina Hingis, has penetrated the world top hundred at an age that is unusually early for these times.
 
Our numerical indicators, discussed next, rest largely on playing results of the last year or so. The numbers, however, fail to identify each player's immediate physical readiness -- in recovering from recent injuries or illnesses and in avoiding fresh ones, for example. Because of such factors, our final predictions, though they are derived largely from the numerical indicators, are not required to follow them rigidly.
 
THE INDICATORS
 
The design of our indicators have been adjusted slightly with growing experience in their use. Here are the leaders in the current calculations for predicting Garros 2014. (The top sixteen raw scores within each indicator are normalized to reach total of 100.)
 
1. Basic Indicator. Playing results of the last 15 months are weighted in accord with years of data measuring how well results at various predictor tournaments have correlated with results at succeeding renditions of Garros. Of the 24 predictor events used here in predicting the men's singles at Garros 2014, the heaviest weighted are Garros 2013, Monte Carlo 2014, and Italy 2014, in that order. Here are the leaders: