Second seed Daniil Medvedev was stunned by qualifier Thiago Seyboth Wild in a big French Open first-round shock.

Medvedev had arrived at Roland Garros in good form and in contention for the world number one ranking.

But 172nd-ranked Seyboth Wild pounced on Medvedev's inconsistency to book a first Grand Slam second-round spot.

"I watched Daniil play since I was a junior and beating him on such a court is a dream come true," the 23-year-old, who had not played a Tour-level match this year, said.

"I tried to use my forehand against his and it worked pretty well. I started cramping at the start of the second set but I used my mental strength to play my best tennis."

"I don't really have words to describe what I felt when I won the match. I was just super happy. It definitely was the happiest day of my life."

In a match lasting four hours 15 minutes, Seyboth Wild recovered from losing his opening service game to take the first set.

But when he missed an overhead to hand Medvedev the second set after he had led 6-4 in the tie-break, it looked as if his chance might slip away - especially when the Russian took the third, having had to stop for treatment on a nosebleed just before serving it out.

But Medvedev, who arrived at Roland Garros fresh from winning his first clay-court title in Rome, was repeatedly undone by his opponent's forehand at key moments, as well as registering 15 costly double faults.

Seyboth fought back in the fourth set, getting an early break to lead 3-0, and forced a deciding fifth set, where he broke the Medvedev serve three times.

He set up match point with yet another brilliant forehand before sealing the biggest victory of his career with - of course - a huge forehand down the line.

Medvedev 'happy' to see back of clay season

Medvedev has often said he used to "hate" clay, with a series of four consecutive first-round exits from Paris in his first four appearances doing little to change his mind.

But a run to the quarter-finals in 2021 and the fourth round last year, plus the title in Rome this month, had him declaring that while he did not quite "love" it, there was definitely now more of a "like" for it.

There was little of that on show on a gusty Philippe Chatrier court, where his frustration - with the umpire, the crowd and himself over his inability to deal with the power of a player whose game had clicked at the best time - was evident.

And there was even less after the match as he declared he was "happy" that his clay season was finished.

"Today, because [of the] wind, dry court, I had a mouthful of clay since probably the third game of the match, and I don't like it," he said.

"I don't know if people like to eat clay, to have clay in their bags, their shoes, the socks, white socks; you can throw them to garbage after clay season.

"Maybe some people like it. I don't."

Medvedev struggled particularly with his serve, winning just 46% of points on his second serve, and Seyboth Wild made the most of this to break twice in the decider. The Russian did retrieve those breaks but not the third and the Brazilian kept his composure while the red dirt was flying around the court to record the biggest upset of this year's tournament.

Seyboth Wild, who usually competes on the second-tier Challenger circuit and had won two titles on clay this year, will face Argentina's Guido Pella or Frenchman Quentin Halys for a place in the next round.

Zverev wins on return to Paris after bad injury

Germany's Alexander Zverev made a winning return to the tournament a year after leaving his Roland Garros semi-final in a wheelchair with a serious ankle injury.

The 26-year-old retired in the second set of his semi-final against Rafael Nadal last year and was out for six months with torn ligaments, but beat South African Lloyd Harris 7-6 (8-6) 7-6 (7-0) 6-1 on his return to Paris.

"It's very, very nice to be back," he said in his on-court interview.

"I was obviously very disappointed with how that tournament finished for me [last year].

"That's why I appreciate it even more when I play in a full stadium and the crowd is behind me. It was just a lot of fun out there."

Zverev, seeded 22nd, will face Slovakia's Alex Molcan next as he bids for a first major singles title.

Also through to the second round is last year's runner-up Casper Ruud, with the Norwegian world number four beating Swedish qualifier Elias Ymer 6-4 6-3 6-2 with a commanding display of baseline power. He will face another qualifier, Italian Giulio Zeppieri, for a place in the third round.

Danish sixth seed Holger Rune was tested in an encounter with American Christopher Eubanks before coming through 6-4 3-6 7-6 (7-2) 6-2. His next match features a tricky opponent in either French former top-10 player Gael Monfils or Argentine world number 42 Sebastian Baez.