The world number 79 from Germany saved two match points en route to a gruelling 6-7, 7-6, 1-6, 7-6, 7-5 win.

Altmaier was on the brink of defeat as Sinner was serving for the match in the fourth set on the Court Suzanne-Lenglen but remarkably turned it around to beat the eighth seed after five hours and 26 minutes.

"Playing every point you can with the best effort, that’s what keeps you in reality," said Altmaier.

"I was just thinking that, and the competition says it all.

"We've had historic matches with so many match points.

"I don’t know if you can call this an 'historical' match, but I think it was one to remember."

Also in the men's singles, Norwegian fourth seed Casper Ruud advanced to the round of 32 with his commanding 6-3, 6-2, 4-6, 7-5 win over Italy's Giulio Zeppieri.

Women's singles defending champion and world number one Iga Świątek cruised into the third round of Roland Garros.

The Pole defeated 102^nd-ranked Claire Liu of the United States 6-4, 6-0.

"I was able to play a little bit better in the second set, and I kind of used first set to get more information and get into the rhythm, but Claire played pretty well," Świątek said.

"I'm happy that I'm into the third round and I have a chance to play more matches here."

She is joined in the next stage by 2019 US Open champion Bianca Andreescu of Canada who downed American wildcard Emma Navarro 6-1, 6-4 after one hour and nine minutes.

Świątek's win was her 30^th of the year and she is currently tied with Kazakhstan's Elena Rybakina for the second-most wins on tour in 2023.

Only Belarusian Aryna Sabalenka has more, with 31.

Competition is set to continue tomorrow with the match of the day pitting first seed Spaniard Carlos Alcaraz against Canada's Denis Shapovalov in the men's singles.