PARIS — Less than a week ago, Jakub Mensik was pushed away from the court in a wheelchair after collapsing to the clay with cramps.

Now the 20-year-old Czech player is in the French Open semifinals.

The 6-foot-5 Mensik used his attacking game to end the run of Brazil's Joao Fonseca with a 6-4,6-3, 7-6 (3) victory in the quarterfinals on Tuesday.

It was Mensik's most convincing performance so far at Roland Garros after struggling physically in the heat wave during the opening week.

After Mensik edged Mariano Navone in a fifth-set tiebreaker in the second round, he fell to the clay after match point and required medical attention on the court after Navone went over to check on him.

Mensik was eventually helped up and limped off the court, then was pushed away in a wheelchair.

Two days later, Mensik still appeared weak when he dropped the opening set 6-0 to Alex de Minaur. But then he won three straight sets.

"After the cramps and super dehydrations, I needed to put as much fluids as I could inside of me," Mensik said after beating De Minaur. "I came back strong enough to compete again on the highest level and on these very cruel conditions."

Mensik also needed five sets to advance in the fourth round against Andrey Rublev.

Then against Fonseca, Mensik won 13 of 15 serve-and-volley points to Fonseca's one in his only try.

"It was one of my best performances so far," Mensik said.

The 19-year-old Fonseca beat 24-time Grand Slam champion Novak Djokovic in five sets in the third round and then eliminated two-time runner-up Casper Ruud in the fourth round.

For a place in Sunday's final, Mensik will face second-seeded Alexander Zverev, who eliminated rising Spanish player Rafael Jodar 7-6 (3), 6-1, 6-3.

Mensik has won just two titles in his career and neither of them came on clay. He beat Djokovic in straight sets in the final of the Miami Open last year for his first title. His second title, in Auckland, New Zealand, this year also came on hard courts.

During Mensik's post-match on-court interview on Tuesday, his mom Katerina Mensikova created a heart shape with her fingers as she looked on from the stands — drawing a chuckle from Mensik.

Mensik wasted six match points in the final game before Fonseca eventually held serve. Then he quickly took control of the tiebreaker.

"The last 20-30 minutes of the match it was just really insane," Mensik said. "I'm happy I managed to stay mentally focused and calm."

Exceeding expectations

Fonseca said reaching the last eight of a major for the first time had exceeded expectations after arriving in Paris with concerns over a recent injury.

"Coming from a little injury and not having any expectations for this tournament and doing a great run, this is a positive week," Fonseca told reporters.

"This tournament gives me more conviction and more confidence to keep going and for sure understanding a little bit more body and my limits."

Fonseca said the fortnight showed him how his body could cope with the physical demands of Grand Slam tennis and reinforced his belief that he was moving in the right direction.

"I never saw my limit yet, but I already know that I can be comfortable with my physique," he said.

"I think it's more comfortable with my game, the way that I'm playing, that my mentality is on the right path... Maybe it's the same Joao, but finding new stuff."

The teenager was full of praise for 20-year-old Mensik.

"His serve is amazing," Fonseca said. "The most important thing is he knows how to play in important moments. He's not afraid.

"Today was not me playing bad. It was all his merit."

Despite the defeat, Fonseca said he would head into the grass-court season encouraged by his performance in Paris.

"Looking forward to reset now," he said. "Going back home, enjoy a little bit with the family and then go again for another swing."

Russia-Ukraine semifinal

Marta Kostyuk and Mirra Andreeva will meet on Thursday for a place in the women's final.

The in-form Kostyuk held her nerve to withstand a comeback from compatriot Elina Svitolina in the first all-Ukrainian women's quarterfinal at a Grand Slam in the Open era, prevailing 6-3, 2-6, 6-2.

The 23-year-old Kostyuk extended her unbeaten run on clay this season to 17 matches to reach her first Grand Slam semifinal.

Andreeva, of Russia, breezed into her second French Open semifinal with a 6-0, 6-3 rout of Romania's Sorana Cirstea, who plans to retire at the end of the season.