WTA roundup: Osaka rallies to reach Stuttgart semis

Top-seeded Naomi Osaka had to fight off Donna Vekic of Croatia to post a 6-3, 4-6, 7-6 (4) quarterfinal victory on Friday at the Porsche Tennis Grand Prix at Stuttgart, Germany.

Osaka trailed 5-1 in the final set before rallying for the victory on the clay courts in two hours, 18 minutes.

"I mean I felt like it just happened really fast. She was 3-0 and suddenly, she was 5-1 and I felt like I took a while to get going," the Japanese star said after the match.

"I didn't feel like I could swing freely. I think I played the best in the first set, and then it just kind of dipped a little bit, but instead of swinging freely I would say I was trying to be more consistent."

Osaka will meet eighth-seeded Anett Kontaveit of Estonia in the semifinals. Kontaveit prevailed 7-5 5-7, 3-0 over Victoria Azarenka of Belarus. Azarenka retired in the third set due to an injured right shoulder.

Kontaveit hit 37 winners, including six aces, to overcome 35 unforced errors.

Sixth-seeded Kiki Bertens earned a semifinal berth with a solid 6-3, 6-4 victory over Germany's Angelique Kerber.

The Netherlands native had 29 winners against 21 unforced errors in the 75-minute match. Kerber had just 11 winners while recording 25 miscues.

Bertens will face third-seeded Czech Republic star Petra Kvitova, who rallied for a 2-6, 6-2, 6-3 win over seventh-seeded Anastasija Sevastova of Latvia.

Kvitova is in the semifinals at Stuttgart for the third time.

TEB BNP Paribas Istanbul Cup

Sixth-seeded Petra Martic of Croatia outlasted Kristina Mladenovic in a marathon match to reach the semifinals on the clay courts at Istanbul.

Martic prevailed 7-6 (4), 4-6, 7-6 (2) in a match that took three hours, 17 minutes, the longest WTA match so far this year.

"The level was good but we couldn't always convert our chances -- and we had many," Martic said after the match. "But I'm just happy I managed to win. I feel pretty tired but adrenaline is still going and keeping me on my feet. I just hope I can recover for tomorrow."

Martic will face Margarita Gasparyan, who was a 7-5, 6-4 winner over fellow Russian Veronika Kudermetova.

Marketa Vondrousova of the Czech Republic claimed her semifinal berth with a dominating 6-1, 6-2 win over Spain's Lara Arruabarrena. Vondrousova will face Czech Barbora Strycova, who registered a 0-6, 7-6 (6), 6-0 victory over Russia's Elena Rybakina.

--Field Level Media