The top-ranked Djokovic lost his serve in game seven and needed to save two set points in order to hold the ninth game at 5-3 down. The 16-time Grand Slam winner broke back for 5-5 against his 20-year-old opponent, who has never won a title while Djokovic chases a 77th.
U.S. Open champion Rafael Nadal, who is battling with his old rival Djokovic for the year-end No. 1 ranking, won 7-5, 6-4 against unseeded Frenchman Adrian Mannarino. The second-seeded Spaniard next faces 16th-seeded Stan Wawrinka, with an 18-3 lead in their career meetings.
"My serve worked very well during the whole match, I think I played at the right level," said Nadal, who had eight aces. "Not easy to come back after a while without being on the tour." The recently married Nadal has played just once since clinching the 19th major of his career — a round robin win against Canadian Milos Raonic at the Laver Cup more than one month ago — but did not face a break point while Djokovic saved four of six he faced.
Djokovic, who sounded croaky when speaking after the match, explained he has been feeling unwell. "The last three days, you know, some things unfortunately caught up with me," Djokovic said, without giving details. "Health-wise not feeling my best. ... It affects your energy, your vitality on the court. Your alertness, attention, endurance, all these different things are affected."
Djokovic, who lost last year's final and last won here four years ago, dropped serve again as Moutet broke back to 4-2 in the second set. But he clinched the victory with a forehand winner down the line on his first match point and next faces Britain's Kyle Edmund, who beat 14th-seeded Diego Schwartzman 7-5, 6-3.
Earlier, Dominic Thiem withstood 30 aces from the big-serving Raonic to win 7-6 (5), 5-7, 6-4. The two-time French Open runner-up saved nine break points out of 10, and then broke Raonic for the first time in the ninth game of the deciding set before serving out the match.
The fifth-seeded Austrian player, who won the Erste Bank Open in Vienna last Sunday for an ATP Tour-leading fifth title this year, next plays Grigor Dimitrov. Seventh-seeded Stefanos Tsitsipas served 13 aces in beating Taylor Fritz 7-6 (3), 6-3. The 21-year-old Greek player next plays Alex de Minaur, a 20-year-old Australian who lost the Swiss Indoors final to Roger Federer on Sunday.
Federer is skipping this tournament, but Nadal and Djokovic are looking to score big points in Paris. Nadal can guarantee the year-end No. 1 position for the fifth time in his career by winning the indoor tournament for the first time, while Djokovic seeks a record-tying sixth year-end finish with the top ranking.
Matteo Berrettini, beaten by Nadal in the U.S. Open semifinals, was one of several seeded players knocked out in the second round. The 10th-seeded Italian lost 6-4, 6-3 to 2008 champion Jo-Wilfried Tsonga of France, who next plays big-hitting German Jan-Lennard Struff.
Another big server was eliminated as 15th-seeded American John Isner — the 2016 runner-up — was downed 7-6 (5), 7-6 (4) by Cristian Garin of Chile despite having 25 aces. Denis Shapovalov of Canada rallied to beat No. 11 Fabio Fognini 3-6, 6-3, 6-3 and plays No. 6 Alexander Zverev next. Wawrinka advanced with a 7-6 (3), 7-6 (5) win over Marin Cilic and improved his record to 13-2 against the former U.S. Open champion.
De Minaur upset No. 9 Roberto Bautista Agut 7-6 (2), 7-6 (1); Dimitrov beat No. 12 David Goffin 7-5, 6-3, and Gael Monfils won 6-4, 7-6 (4) against Benoit Paire.
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