Australia's Adam Walton has played the match of his career to send former world number one Daniil Medvedev packing at the French Open.

In unusually hot conditions that made the courts faster than usual, Medvedev struggled in a five-set loss to his 97th-ranked opponent.

Walton, who received a wild card invitation from tournament organisers, beat Medvedev 6-2, 1-6, 6-1, 1-6, 6-4. It was Medvedev's second-straight first-round exit here and third in four years.

"He was playing pretty well, making a lot of first serves [early in the fifth set], and was liking my ball, so I knew I just had to hang tough," Walton said.

Walton said he felt the conditions might have played to his advantage.

"It's definitely hotter than previous years that I've played here," Walton said.

"But we grow up in the heat [in Australia]. We like the heat, so it makes the ball move faster through the air, which I think helped my game today, so I really like it when it's hot in Paris."

Medvedev said he knew why he struggled at the French Open, but he did not want to share what he knew.

"I know why I don't really play my best in Roland Garros, but if I say it, it's [making] excuses," he said. 

"So I keep it to myself."

Walton will face American Zachary Svajda in the second round. 

Popyrin back to the drawing board

Alexei Popyrin was left wondering where he goes next after a tame first-round French Open exit.

Popyrin was beaten 3-6, 6-3, 7-6 (7-3), 7-5 by Svajda.

Asked what happens next, the 26-year-old was too dismayed to offer any clear vision.

"We'll see. I don't know yet, I'm not sure, it's too close to the match," Popyrin said.

"I'm still a little bit emotional, so I don't want to make an emotional decision at all, in terms of what I'm going to do, in terms of schedules, in terms of anything, actually.

"So I'm just going to take some time, cool off a little bit, and then we'll see what I'll do."

AP/AAP