PARIS (AP) — So dominant this month when she won the Italian Open, Karolina Pliskova looked out of her comfort zone on the red clay of Paris on Friday.

The second-seeded Czech struggled in the longer rallies of a 6-3, 6-3 loss to No. 31 Petra Martic in the third round of the French Open, bending over in exhaustion after extended points on Court Philippe Chatrier.

"The court is pretty slow, so you just have to play some extra shots," Pliskova said. "I was a little bit ... passive, maybe not that fast. My serve wasn't really working. I don't think she did much wrong today. ... I just did too many mistakes."

Pliskova's loss meant that Naomi Osaka will hold onto the No. 1 ranking after the tournament.

It was Martic's tour-best 14th win on clay this season. The Croatian has not dropped a set in her opening three matches.

"The key was to focus on my game and try to dictate instead of letting her dictate, which is her biggest strength," Martic said.

On Court Suzanne Lenglen, 12th-seeded Anastasija Sevastova saved five match points before rallying to beat No. 20 Elise Mertens 6-7 (3), 6-4, 11-9.

Mixed up by Sevastova's spins and vast array of shots, Mertens fell to the clay three times late in the third set, leaving almost her entire body covered in dirt — her arms, her legs and her shirt.

"It was probably the longest match in my career," Sevastova said in an on-court interview after the match of 3 hours, 18 minutes. "Thanks to her, because without her we wouldn't play this match."

Also, last year's semifinalist Madison Keys beat Pricilla Hon of Australia 7-5, 5-7, 6-3 in a second-round match carried over from Thursday, and 19-year-old Marketa Vondrousova eliminated 28th-seeded Carla Suarez Navarro 6-4, 6-4 to reach the fourth round of a Grand Slam tournament for the second time after last year's U.S. Open.

In a men's match extended from Thursday, Martin Klizan beat 22nd-seeded Lucas Pouille 7-6 (4), 2-6, 6-3, 3-6, 9-7.

Later, Roger Federer was playing 63rd-ranked Casper Ruud, the son of a player who was in the field when the 20-time Grand Slam champion made his debut in Paris in 1999.

With seeded players going head-to-head for the first time at this year's tournament, 11-time Roland Garros champion Rafael Nadal was to play No. 27 David Goffin.