Spain's Carlos Alcaraz reached the French Open third round but suffered a worrying loss of form midway through his match against Dutch qualifier Jesper de Jong before winning 6-3 6-4 2-6 6-2.
The third seed was forced to work hard for a two-set lead under the Court Philippe Chatrier roof but 176th-ranked De Jong refused to be intimidated and extended the match as Alcaraz suffered a third-set slump.
An error-strewn Alcaraz continued to struggle as the first four games of the fourth set all went against serve with the 21-year-old becoming increasingly frustrated on court.
But Alcaraz regained some control in the nick of time to hold serve for a 3-2 lead and he broke De Jong in the next game as his gritty opponent finally began to run out of steam.
There was some relief as Alcaraz accelerated towards victory and De Jong netted a forehand after a little more than three hours to end an absorbing contest.
Elsewhere, former French Open runner-up Stefanos Tsitsipas beat German Daniel Altmaier 6-3 6-2 6-7(2) 6-4 in two hours and 43 minutes.
In the women's competition, Tunisia's Ons Jabeur beat Colombia's Camila Osorio 6-3 1-6 6-3 in a roller-coaster match in humid conditions under the roof on Court Suzanne-Lenglen to move into the third round.
Jabeur hardly put a foot wrong in the opening set but she allowed Osorio to get back into the match with a poor second-set performance before raising her intensity in the third to secure the win.
Meanwhile, former Australian Open Champion and French Open finalist Sofia Kenin breezed into the third round with a convincing 6-3 6-3 victory over home hope Caroline Garcia.