Sinner recovers to reach French Open quarter-finals
The 79th-ranked Moutet, the last Frenchman left in the draw, rattled off the opening five games of the match before Sinner wrested back control and eased to a four-set victory.
"It was very tough for me. I think he played very, very well in the first set, so I had to adjust a little bit," said Sinner.
"He plays different than most of the opponents, he's also a lefty and you don't play so many times against left-handers."
Sinner's seventh Grand Slam quarter-final appearance represents the most for an Italian man in the Open era. It is the first time he has made the last eight at Roland Garros since the pandemic-delayed 2020 edition.
He will play Bulgarian 10th seed Grigor Dimitrov for a spot in the semi-finals.