If ever you were uncertain that fortunes change quickly in tennis, this year's French Open ought to convince you. When the tournament began, Rafael Nadal seemed incapable of losing on clay unless he had played a four-hour match the day before. Then along came some worrisome knee pain and a giant pain in the rear end named Robin Soderling. Roger Federer couldn't beat Nadal in Paris, and then he didn't have to—and he didn't have to beat Novak Djokovic or Andy Murray, two other Federer killers, either. On the women's side, 2008 titlist Ana Ivanovic went from a champ with unlimited potential to a straggler with an uncertain future. Svetlana Kuznetsova, who has been the former and the latter, made another surprising turn and became a champion again. What does it mean for the rest of the season and beyond? A look at the implications of what transpired in Paris for the 2008 and 2009 winners:

Roger Federer
Federer has played under immense pressure for years. Would he tie or break Pete Sampras' record of 14 major titles? Would he ever win the French Open? Federer, who will become a father this summer, can now breathe easy, but I don't expect him to slack off. Tennis players tend to respond to great achievements in one of two ways: Lose motivation and fade away, as Mats Wilander did when he won three majors in 1988 (he never won another one), or play freely and prosper, as Andre Agassi did when he completed a career Slam at the French Open in 1999 (Agassi won three more majors and reached two other finals). I expect Federer to be more Agassi than Wilander. It took perhaps the best performance in the history of the game to beat Federer at Wimbledon last year; can someone, even a healthy Nadal, pull it off again? Without any worries, Federer might well sweep the rest of the majors and end 2009 atop a heap of 16 Slams and unquestioned status as the greatest who ever lived.
Prediction: He wins Wimbledon but not the U.S. Open, where he is five-time defending champion.

Svetlana Kuznetsova

Many tennis writers (including yours truly) considered Kuznetsova the best of the Russian empire when she won the U.S. Open in 2004. She's got the most versatile game, a solid serve, and better hands at net than anyone of the other Russian players. It wasn't long, though, before we all realized that her mind and confidence were shakier than her strokes. Will that change now that she has won a second major title? I'm not convinced, but Kuznetsova will remain dangerous, and on any surface. Still, I wouldn't be surprised if she never wins another major.
Prediction: She wins the French at least once more, but will never win another major not played on clay.

Rafael Nadal
Nadal went into Paris as the overwhelming favorite and a legitimate candidate for the first Grand Slam since Rod Laver; now he might not defend his Wimbledon title. The question on everyone’s mind is, “How bad are his knees?” Nadal’s website has been precise in terms of medical diagnosis—he “suffers from insertion tendonitis in the superior end of both kneecaps with a light osseous edema”—but unclear on his prognosis, or if surgery might be required if physical therapy doesn’t produce results. Nadal’s absence in the French Open final doesn’t taint Federer’s victory in the least. Still, any prolonged absence will hurt the men’s game, which is at its peak at the moment. We can only hope that Nadal’s inspired run at the French Open and Wimbledon last year, when he played the best tennis I’ve ever seen, won’t be the pinnacle of a too-brief career.
Prediction: He struggles (by his standards) until next year, when he wins his fifth French Open.

Ana Ivanovic

In February, Ivanovic hired Craig Kardon as her full-time coach. After losing in the fourth round of the French Open, she dumped him, raising new doubts about the direction of her game. No one thought Ivanovic would become the dominant player on the tour (her game has too many holes for that). But her decline since winning last year’s French Open has been surprisingly steep for a woman of such talent. Ivanovic takes a lot of risks (flat strokes and lots of angles) and one can’t play that style of tennis without conviction. She’ll be working with team Adidas again, which (under Sven Groeneveld’s guidance) helped her win her first major. It might be a while before she wins a second one. Perhaps Kuznetsova can give her some encouragement.
Prediction: She wins the Australian Open in 2011.

Tom Perrotta is a senior editor at TENNIS magazine.