Coming from a player whose mental strength has often been questioned, the gesture spoke volume.

The top-ranked player indeed showed solid nerves to turn things up after a really bad start in her French Open quarterfinal on Wednesday. After 2 hours and 14 minutes, Halep rallied past the 12th-seeded Kerber 6-7 (2), 6-3, 6-2 and reached the French Open semifinals for the third time.

"It was really about the mental," Halep said. "So I think that's why I won today. My head won it."

She next faces third-seeded Garbine Muguruza, who thrashed Maria Sharapova 6-2, 6-1 in a matchup of past French Open champions.

Halep went all out in the first set against Kerber, but her bold strategy backfired badly as she hit 30 unforced errors. After trailing 4-0 in the opening set, Halep fought back to force a tiebreaker but briefly lost her focus to drop the set after losing five consecutive points.

"After the first set I just stayed strong, I did not give up at all," Halep said. "I missed a lot at the beginning of the match. I tried to do too much. Then I changed a little bit of tactics and it worked."

Halep broke at the start of the second set and then Kerber dropped her serve again in the ninth game. In the decider, Halep came to the net more often to finish points and opened up a 4-1 lead. She broke again in the eighth game to seal the match.

The two met in the semifinals earlier this year at the Australian Open, with Halep prevailing 9-7 in a third set there. That match lasted a total of 35 games, marking the longest women's semifinal at the Australian Open in the Open era.

Halep is still chasing her first Grand Slam title after several near-misses. She led Jelena Ostapenko by a set and 3-0 in last year's final at Roland Garros, but then fell apart and eventually lost to the unseeded Latvian in her second French Open final.

Halep reached the semifinals in a Grand Slam event for the sixth time in her career, matching Ilie Nastase for the most by a Romanian male or female in the Open era.

"I don't feel I'm favorite for this match, because she's played better than I have this year," Muguruza said of her next match against Halep. "She loves clay. She loves Roland Garros. She's shown it."

The No. 3-seeded Muguruza had lost all three previous meetings against Sharapova, who won two of her five Grand Slam titles at Roland Garros. This time, she needed only 70 minutes to eliminate Sharapova and dominated her with superb returning, breaking the former No. 1 a half-dozen times.

Muguruza has not dropped a set so far in this year's tournament as she seeks a second championship in Paris and third major trophy overall. The Spaniard won the French Open in 2016 and Wimbledon last year.

"I think she did a lot of things better than I did. I think she was the aggressive one," Sharapova said. "She had a lot more depth in the ball. I think my shots were a lot more forced. She served a lot better than I did."

According to ESPN Stats & Information, the last woman to win the French Open without dropping a set was Justine Henin, who did so in back-to-back years in 2006 and 2007.

Sharapova looked far from her best right from the start, double-faulting three times to get broken in the opening game. She ended up with six double-faults and 27 unforced errors, 12 more than Muguruza.

Muguruza raced to a 4-0 lead and never looked back. She is 48-2 in majors after winning the opening set.

"I was focusing on winning every point, every game," Muguruza said. "The score doesn't really matter."

Sharapova didn't need to play a point in the fourth round, because Serena Williams pulled out of their much-anticipated match with a pectoral injury. Muguruza essentially got that round off, too: Her opponent, Lesia Tsurenko, retired with an injury after only two games.

"I guess, you know, on paper, it's a step in the right direction," Sharapova said. "... Coming into this part of the year, I was losing a few first-round matches, matches that I wanted to be winning, of course. But to have had the victories that I have had, to have the results that I have, obviously moving a step in the right direction.

"But today was certainly not one of those steps."

It ranked among one of the most lopsided losses ever suffered by Sharapova in her Grand Slam career. Only a loss to Dominika Cibulkova in the 2009 quarterfinals here, in which she won only two games, was worse.