Moutet, who has one of the most unorthodox games on tour, deployed the underarm serve on several occasions as he attempted to upset Sinner on Court Philippe-Chatrier, but it backfired at a key stage of the fourth set.
Trailing 3-1 in the set and down two sets to one, he was adjudged to have foot faulted in the first point of the game and made his displeasure known to the umpire.
He argued his case as boos rang out from the stands but replays conclusively showed the right decision had been made by the line judge.
“I didn’t!” Moutet repeatedly said, raising his hands to the Parisian sky in dismay.
“It’s a foot fault,” Tim Henman said on commentary. “His foot is on the line. It’s 100% the correct call.”
He would eventually go on to lose the point and the game as his protests continued.
“Is he looking for an excuse?” Henman was asked, with the Brit replying: “I think he’ll look at this after the match and just feel a bit stupid.”
Moutet would then gesture to break his racquet when he dumped a drop shot into the net at 30-15 but it is these displays of emotion that make the Frenchman such an entertaining player to watch.
His full array of skills was on show in the first set as he won the opening five games and came within a point of bagelling the world No. 2, but Sinner would eventually find form and prove too strong.
After losing seven of the first nine games, he won 18 of the next 23 to extinguish the challenge of his opponent and set up a last-eight meeting with Grigor Dimitrov, with a potential showdown with Carlos Alcaraz in the semi-finals awaiting.