The next time we see them competing, at Wimbledon in two weeks, Nadal will be merely a serious contender, while Williams will be the unquestioned favourite.
Both have a won-loss record of 43-2 in 2013. Nadal has won 22 matches in a row. Williams has won 31 straight, the longest single-season run on the women's tour in 13 years.
Nadal's Grand Slam title total now stands at 12, tied with Roy Emerson for the third-most in the history of the men's game, behind only Roger Federer's 17 and Pete Sampras' 14.
Williams is up to 16 major singles trophies, sixth-best among women, with Chris Evert and Martina Navratilova right above her on the list at 18.
Now comes the shift from the clay of Roland Garros to the grass of Wimbledon, and that is where the similarities end. Williams is a five-time champion at the All England Club, including a year ago, and the way she's playing at the moment, there is little reason to anticipate anyone beating her there this time. Nadal, despite his recent form, is only one of a group of men who can think of themselves as possible champions, along with No. 1-ranked Novak Djokovic, No. 2 Andy Murrray and No. 3 Federer.
"The objective now is to celebrate tonight," Toni Nadal, Rafael's uncle and coach, said Sunday, when his nephew won his eighth French Open championship by easily beating David Ferrer 6-3, 6-2, 6-3 in the final, two days after outlasting Djokovic 9-7 in the fifth set of a wonderful semifinal, "and then we will see if he plays well at Wimbledon."
Even the Nadals acknowledge that Rafa is not quite as superb on grass as he is on clay. How could he be? He is 59-1 in the French Open, with four titles in a row from 2005-08 and another four in a row from 2010-13, and the only man to claim eight titles at the same major tournament.
That said, he's done well at Wimbledon, winning it in 2008 and 2010, and losing in the final to Federer in 2006-07 and to Djokovic in 2011.
A year ago, though, Nadal fell in the second round against Lukas Rosol, who was ranked 100th at the time. That would be the last match Nadal played for about seven months because of a painful left knee, an absence that saw him skip the London Olympics, the U.S. Open and the Australian Open and is the reason he's ranked No. 5 this week.
"Some weeks I didn't feel well, but the last couple of weeks I start to feel ... better," Nadal said Sunday. "I am still going week by week, day by day."
He usually likes to prepare for Wimbledon by playing in a grass-court tournament during the week right after the French Open. But this time, Nadal withdrew from the field in Halle, Germany, and opted for rest, instead.
"That's not the ideal situation before a Grand Slam like Wimbledon that is on grass," Nadal said. "The conditions are very different."
What he will do is head to the practice court, to keep on getting better, just as he's done for years.
His serve used to be a real weakness, for example, so Nadal and Uncle Toni studied ways to speed it up and add variety.
At first, he found grass to be problematic, but his accomplishments at Wimbledon are ample proof that he figured out a way to overcome that, too.
"You can improve always, in every way," Nadal said. "And in tennis, for sure, you can keep improving."
Williams expressed a similar sentiment after her 6-4, 6-4 victory over defending champion Maria Sharapova in the women's final Saturday in Paris.
Unlike Nadal, she's had her issues with red clay: After winning the French Open in 2002, it took Williams 11 years to get her hands on a second trophy. And unlike Nadal, she's excelled more on other surfaces, with those five Wimbledon championships, plus five on hard courts at the Australian Open, and four on hard courts at the U.S. Open.
Tough as her serve was to handle at the French Open these last two weeks — she hit 10 aces against Sharapova, for example, including three in the last game — it should only be more effective on grass, where balls skid instead of clay's higher bounces.
After her own stunning early exit at a Grand Slam tournament last year — at Roland Garros, in the first round, to a woman ranked 111th — Williams immediately went about fixing things. She stuck around Paris to practice for Wimbledon at coach Patrick Mouratoglou's tennis academy and has gone 74-3 since, winning three of the last four major titles, plus gold at the Olympics.
"It really was a shock for her. She really worked on rebuilding herself to become perhaps stronger than ever," Mouratoglou said.
And Williams insists that she is willing to find new areas to work on, which might not be comforting to other women hoping to knock her from No. 1.
"The day I feel that I cannot improve, it's going to be a problem for me. I'm going to have to really debate whether I should keep playing," said Williams, who almost always skips Wimbledon tuneup tournaments. "But I feel like, as of now, I can do a lot of things better. I can be better. I feel like I can be more fit. There's still a level of improvement that I can reach."
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Howard Fendrich covers tennis for The Associated Press. Write to him at hfendrich(at)ap.org