PARIS — Juan Martin del Potro frittered away four chances to claim a gripping opening set against No. 1 Andy Murray at the French Open, including one with a “How did that happen?!” double-fault in a tiebreaker.

Then, on Murray’s third set point, del Potro made another mistake, pushing one of his intimidating, grunt-accompanied forehands wide. After walking up to check the ball’s mark on the clay – a line judge and the chair umpire confirmed it was out – del Potro leaned forward on the net, head bowed, the very picture of despair. He remained there for several seconds, delaying the court sweepers’ between-set duties.

Eventually, del Potro went to his seat and covered his face with a white towel. That set was gone and, soon enough, his first appearance since 2012 at Roland Garros was over entirely with a 7-6 (8), 7-5, 6-0 loss to Murray in the third round.

“Too much frustration,” said del Potro, the 2009 U.S. Open champion, who has endured a series of operations on his left wrist, making two-handed backhands problematic. “I couldn’t believe I lost that set.”

Neither, really, could Murray, who noticed how crestfallen his opponent was after that vital set. It lasted nearly 1½ hours, filled with extended rallies and terrific shotmaking.

“Look, regardless of how someone reacts, necessarily, you still have to expect that they are going to come out and start the (next) set strong,” said Murray.

But under a cloud-filled sky at Court Philippe Chatrier, Murray was looking more and more like the top-ranked player that he is.

“I’m starting to feel better,” Murray said. “I had struggled the last six or seven weeks coming in.”

After the nearly 3-hour tussle in a rematch of the 2016 Rio Olympics final he won, Murray declared the last two sets the best he’s played on clay this season. His major titles have come on faster surfaces at Wimbledon and the U.S. Open, but Murray was the French Open runner-up last year.

The 2015 champion in Paris, Stan Wawrinka, joined Murray in the fourth round, a 7-6 (2), 6-0, 6-2 winner against 28th-seeded Fabio Fognini. Next for Wawrinka: No. 15 Gael Monfils or No. 24 Richard Gasquet, a pair of Frenchmen whose match was suspended in the first set because of rain that washed out play in the evening.

Other men advancing before the downpour: 2014 U.S. Open champ Marin Cilic, Kevin Anderson and Fernando Verdasco.

Victories by Alize Cornet and Caroline Garcia gave France three women in the fourth round for the first time since 1994 (Kristina Mladenovic advanced Friday). Cornet and Garcia will meet for a quarterfinal. Also into the fourth round: 2014 runner-up Simona Halep and former No. 1 Caroline Wozniacki. Four women’s matches didn’t begin before the wet weather.

Murray vs. del Potro provided the most enticing matchup, a pair of past major champs providing high-quality play and intense competition.

Del Potro’s first set point came in the eighth game, up a break at 5-3, but he missed a return off Murray’s 80 mph second serve. The next came at 5-4, but he netted a backhand, then double-faulted to grant a break point that Murray claimed with a forehand winner. The third arrive at 7-6 in the tiebreaker – the excruciating double-fault. The last was at 8-7, a forced error on a forehand that was the point’s 18th stroke.

Later, del Potro got anti-inflammatory pills from a doctor to help with a bothersome groin muscle, although he said his biggest issue was Murray.

Del Potro lauded Murray’s adjustments – new returning angles, more and more leg-sapping drop shots, even attacking the 6-foot-6 Argentine’s forehand – as the match wore on, saying: “Andy is one of the smartest guys on the circuit, and he knew what my weak points were.”

An appreciative and enthusiastic crowd chanted “Delpo! Delpo!” – his nickname, etched in fluorescent yellow type on the back of black sneakers. Spectators repeatedly gasped in unison at some of the 29th-seeded del Potro’s massive forehands, usually accompanied by a loud exhale.

Asked how he felt about the fans’ response to his forehands, del Potro joked: “I like (it) a lot. I think they’re scared a little bit.”