Rafael Nadal has lost just once in 67 career matches at the French Open, but has been defeated five times on clay this season, his most on the surface since 2004. (Patrick Kovarik/AFP/Getty Images)

How do you say tipping point in French? How about this: Roland Garros.

Every so often historical plot lines converge on an event. The French Open, which begins Sunday on the red clay of Paris, has that heightened sense of import and intrigue. The results from the 15-day tournament could cast players in a different light, or send careers pinballing in new directions.

●Will No. 1 Novak Djokovic, so dominant this season, complete a career Grand Slam and nudge further into the Greatest of All Time debate with a ninth major and first in Paris?

●Can No. 1 Serena Williams, equally imposing in 2015, capture a 20th Slam — sniffing distance from Steffi Graf’s Open-era record of 22?

●Will Andy Murray capitalize on his newfound success on clay, including his first two titles on the surface this month?

●Can Maria Sharapova continue her astounding late-career transformation on dirt and win a third title in four years?

But the biggest narrative fork faces nine-time champion Rafael Nadal.

The soon-to-be 29-year-old hits Paris more vulnerable than — well, pretty much ever, or at least since he was a leaping, pirate-panted, fist-pumping teenager. Synonymous with clay-court savoir-faire, Nadal has tasted defeat just once in 67 matches at the French Open (in 2009 to Robin Soderling in the fourth round). But following a wrist injury and appendectomy last year, he hasn’t been able to summon his best form, even on the surface that has always proved a balm to his injury or confidence woes.

“Obviously today I’m not as good” as before, the jarringly transparent Nadal said this month after falling to Murray in the Madrid final — one of five losses on clay this year, the most he’s had in a season since 2004.

On Friday, the draw didn’t make his path to a 10th crown any easier. Seeded sixth, his lowest ever in the tournament, Nadal could face nemesis Djokovic in the quarterfinals. If the grinding and increasingly injured player departs without the title, it could set in motion a more insidious psychological slide.

“That would be his downfall,” said ESPN’s Patrick McEnroe in a conference call with reporters Tuesday.

Of course, there are sock loads of clay-smeared tennis to be played before that comes to pass, and plenty of capable spoilers eager to see history stalled or redirected.

Djokovic, now married and a father, has been a man on a mission. He will be the heaviest favorite in Paris since the start of the Nadal era a decade ago. The Serb, who turned 28 Friday, captured his eighth major at the Australian Open and is 35-2 this season with an ATP Tour-leading five titles.

The two-time French Open finalist is riding a 22-match winning streak heading into Paris, where is he hoping to complete a career Grand Slam and keep alive his chance at a calendar-year Slam — something no man has accomplished since Rod Laver in 1969. But the Serb is 0-6 vs. Nadal in Paris, including the last three years, two of them finals (2012 and 2014).

“Regardless of that I think he still is playing his best tennis on clay courts in Paris,” Djokovic told reporters on Friday, playing down Nadal’s demise. “He has lost only one match in his entire career here. I think that record speaks enough about his level of play.”

Williams, the champion in 2002 and 2013, has been equally impressive. She has lost just once in 2015 and is gunning for a third consecutive major following victories in Australia and the U.S Open. She is most vulnerable, however, on clay, where her powerful shots and potent serve don’t have the same pop as on grass or hard courts. At 33, she is prone to off days, such as last year’s shocking 6-2, 6-2 second-round defeat to Garbine Muguruza of Spain.

Her clay-court season has been truncated. She lost to No. 4 Petra Kvitova in the Madrid semifinals and withdrew from Rome with an elbow injury, a move she called precautionary. She has played just a handful of matches on dirt and wasn’t handed an easy draw. Her path includes possible matchups with former No. 1 Victoria Azarenka in the third round, sister Venus Williams or American Sloane Stephens in the fourth round, close friend Caroline Wozniacki in the quarterfinals and Kvitova in the last four.

But Serena, the oldest No. 1 in WTA history, does not look like she is ready to relinquish the ranking she has held since February 2013 as she chases down Graf.

“The minute I step on the court, and especially during a match, I just become a different person,” she said Friday.

Should she falter, No. 2 Sharapova will likely be there to reap the benefits. Once so uncomfortable on clay she likened herself to a “cow on ice,” the go-for-broke Sharapova has improved her defense and added an effective drop shop. On Friday, the 28-year-old Russian called her evolution on clay “a big surprise and really incredible achievement personally for me.”

Coming off a third title in Rome this month, the 2012 and 2014 French Open champion has rounded into form for another title run. She is a favorite, along with 2014 runner-up and No. 3 seed Simona Halep of Romania, who is in Sharapova’s half of the draw.

But her biggest challenge is Serena Williams. The American has beaten Sharapova 16 consecutive times since 2004, including the 2013 French Open final and this year’s Australian Open final.

Scotland’s Murray, a 2014 semifinalist, is on the short list of title threats after winning his first two tournaments on clay this month, including a thumping of Nadal in the Madrid final. A former U.S. Open and Wimbledon winner, Murray always had the tools for clay — superior movement, variety of shot, dogged stamina. Under the influence of French coach Amelie Mauresmo, the No. 3 seed can’t be counted out even if his credibility on clay is newly won.

American prospects beyond Williams are slim. It would be a surprise to see one in the second week. Among the hopefuls are 15th-seeded Venus Williams and 41st-ranked Stephens, who reached the fourth round two years ago. But not both: They meet in a marquee first-round clash.

The top-seeded American man is towering John Isner at No. 16, who will try to become the first Yank since Andre Agassi in 2003 to reach the French Open quarterfinals. But the future is coming. Frances Tiafoe, 17, will make his Grand Slam debut after earning the U.S. Tennis Association’s wild-card entry. The Riverdale, Md., native will face 35th-ranked Martin Klizan of Slovakia.

In the present, the buzz about a true Grand Slam is running high. No players since Jennifer Capriati in 2001 and Jim Courier in 1992 have emerged with even the first two legs of a calendar-year Slam.

Djokovic and Serena are poised to do so. With grass and hard courts their dominant surfaces, the chase for the holy grail of tennis could be on.

Most eyes before then will be on 14-time major winner Nadal.

“I would love to arrive to that match,” said Nadal during Friday’s pre-tournament news conference about a meeting with Djokovic in the quarterfinals.

Few would expect anything less.