PARIS -- Rafael Nadal's glorious French Open career very likely came to an end as the 14-time champion suffered his first ever opening-round-defeat on Monday, losing to Alexander Zverev in three straight sets.

Women's defending champion Iga Swiatek kicked off her campaign in style in an earlier action at the Philippe-Chatrier Court as she dismissed French qualifier Leolia Jeanjean 6-1, 6-2 to extend her winning streak at Roland Garros to 15 matches.

Fourth-seeded Zverev handed Nadal a 6-3, 7-6(5), 6-3 defeat in the most mouthwatering clash of the first round, maybe also the most remarkable one of this stage in the tournament's 134-year history.

The 27-year-old German became the first man to defeat Nadal before the fourth round at Roland-Garros and joined Robin Soderling and Novak Djokovic as the third man to defeat Nadal on the Parisian clay.

"To be honest I don't know what to say," Zverev said on court after his win, before handing the mic to the Spanish legend. "First of all, thank you Rafa, from all of the tennis world. It's such a great honour. I've watched Rafa play all my childhood, and I was lucky enough to play Rafa when I became a pro, I was lucky enough to play him two times on this beautiful court."

"Today is not my moment, it's Rafa's moment," Zverev added.

Nadal, ranked 275 at the moment, had never played Roland-Garros unseeded, and never faced a top-10 player in the first round. He had also never lost consecutive matches on his beloved clay, but Zverev changed all that with a command performance.

"It's true that the first round has not been an ideal one," Nadal said after the match. "I had my chances but it was not enough against a great player like Sascha."

As soon as the draw was made, the talk of the red dirt major was this highly-anticipated showdown since the Spaniard legend has indicated on multiple occasions that this year is likely to be his last season competing on the professional tennis circuit.

Zverev's aggressive play set the tone in the first set. The two-time ATP Finals champion took the action to his opponent, hitting 15 winners compared to five for Nadal in the opener.

Nadal faced two break points early in the second set to fall into a deep deficit despite that chants of "Rafa! Rafa!" were heard in and outside the stadium. After digging out of trouble, he conjured memories of his very best tennis to claim a service break and lead by 3-2.

But his rival responded quickly with another break before claiming a tense tiebreak to take a two-set lead.

After Nadal missed a final shot on match point, Zverev gave a muted celebration out of respect for the 22-time major champion. They enjoyed a warm greeting at the net.

"The amount of feelings that I had on this amazing court during all my tennis career is just unbelievable," Nadal said. "I never dreamed I would be here at almost 38 years old, with all the success I had here, winning so many times - it is something that I never dreamt of.

"For me, it's difficult to say what will happen in the future. It's a big percentage that I won't be back at Roland-Garros, but I can't say 100 per cent. I enjoy playing here, I like travelling with the family, and my body is feeling a little bit better than it did two months ago."

For now, Nadal will look to continue testing himself against the best players in the world, with plans to be back in Paris for the 2024 Olympic Games.

World No.1 Swiatek opened her title defence with a trademark performance, thriving as the frontrunner to dispatch local underdog Jeanjean in just one hour.

The Polish arrived at Roland-Garros on a 12-match winning streak off the back of collecting WTA 1000 titles in Madrid and Rome.

"It feels like home here," the three-time champion said. "For sure, these last tournaments gave me a lot. I managed to play good tennis in any conditions, in any circumstances, I'm really proud of myself, I don't want to take anything for granted. Every tournament is a different story, a different chapter and I'll be just focused on the next match."

Reigning Australian Open champion Jannik Sinner also clinched a straight-set victory as the Italian beat American Christopher Eubanks 6-3, 6-3, 6-4 to progress.

Home favourite Varvara Gracheva produced the biggest upset of the first round so far as the world No.88 came from a set down to defeat No.6 seed Maria Sakkari 3-6, 6-4, 6-3.

Sakkari is the first Top 10 seed to fall through the first two days of the tournament. Reigning Wimbledon champion and No.5 seed Marketa Vondrousova dropped just four games in her opening victory over Rebeka Masarova, winning 6-1, 6-3 to advance.