For years and years — a full decade, in fact —
This season, his far-poorer-than-usual results on red clay and acknowledged crisis of confidence are generating talk that his reign at Roland Garros might be about to end.
When the season's second major tournament begins Sunday, the lefty from Spain will not be the favorite, despite what he's done in the past. Instead,
"Nadal has shown some weakness this year, both physically and mentally, that we just haven't seen from him, and I think that's turned the light on in the locker room for some other players," U.S. Davis Cup captain Jim Courier, a two-time French Open champion in the 1990s, said in a telephone interview. "There are players now who think they can get him, and I don't know that, other than maybe Novak, that was necessarily the case before."
There are other story lines to watch, as always.
Yet nothing should be as fascinating as following the paths of Nadal and Djokovic.
So far in 2015, Nadal is 17-5 on clay. Not terrible, but certainly not up to his usual standards.
This is a guy who went 126-4 on the surface from 2006-10. He last lost more than three clay matches in a single season all the way back in 2003.
His heavy topspin forehand hasn't been as reliable. He's been less aggressive. Courier sees movement that's not as fluid too, with a longer, less powerful stride.
There are other issues for Nadal, whose 14 Grand Slam titles are tied with Pete Sampras for second-most among men, behind Federer's 17. His only French Open loss came against
Humility long has been a Nadal trademark, but he's been unusually frank about feeling nervous and lacking self-belief.
"I'm still playing with too much nerves for a lot of moments, in important moments, still playing a little bit anxious in those moments," Nadal said in late March.
"But I'm going to fix it. I don't know if in one week, in six months, or in one year, but I'm going to do it."
In 2014, he arrived at Roland Garros with three losses on clay and appeared vulnerable to some, then began slowly.
By the end of the 15-day tournament — surprise! — Nadal had collected yet another trophy.
"Players carry scar tissue with them from difficult defeats," Courier said. "Nadal has been the best I've seen at putting minor defeats and minor issues behind him and just looking ahead to the next point.
"But it feels like this year he's carrying a little bit of the weight of past misses and isn't looking ahead with quite the same crystal-clear vision he's had. You can see a little frustration in his eyes at times, something that we would never really see before."
Chris Evert, whose 18 Grand Slam titles included seven at the French Open, thinks opponents notice.
"Look at his face," Evert said in a telephone interview. "He seems baffled: 'Why can't I hit those winners like I used to?'"
If Nadal truly is different this time around, Djokovic seems best positioned to take advantage.
In 10 previous appearances at Roland Garros, Djokovic exited six times against Nadal, including each of the last three years — twice in the final, once in a semifinal.
Djokovic can become the first man since Courier in 1992 to win the Australian Open and French Open in the same year, moving halfway to a calendar-year Grand Slam.