BERLIN -- World No.2 Coco Gauff advanced to her second ecotrans Ladies Open semifinal after No.10 Ons Jabeur retired with illness.

Gauff edged Jabeur in a tightly contested a 68-minute set, winning 7-6(9). After dropping the opening set, Jabeur was assessed by the trainer and doctor and retired.

Berlin: Draws | Schedule | Scores

It was a disappointing end for Jabeur, who gamely saved a total of 10 set points to take Gauff to the brink in the first set. The American saved two set points in the tiebreak, but ultimately prevailed to advance to her third career grass-court semifinal. 

"I was happy with how I was able to play," Gauff said. "Of course, I send my best wishes to Ons. It's not the way you want to finish a match, especially with someone who is so nice on and off the court."

Gauff will face No.5 Jessica Pegula in the semifinals. Pegula closed out her rain-interrupted quarterfinal against Katerina Siniakova to win 7-6(2), 3-6, 6-3 and advance to her first grass semifinal of her career.

Jabeur's was the second retirement of the day in Berlin. No.24 Anna Kalinskaya advanced to her first grass-court semifinal after No.3 Aryna Sabalenka retired due to a shoulder injury. Earlier in the week, reigning Wimbledon champion Marketa Vondrousova (right hip injury) and No.4 Elena Rybakina (abdominal pain) also retired mid-match. 

Kalinskaya led 5-1 in the first set before the reigning Australian Open champion decided not to continue. Sabalenka called a medical timeout to have her shoulder and neck area assessed and treated at 4-1, and tried to play through the injury. But after another game, the No.2 seed made the decision to retire.

It is the first injury retirement of Sabalenka's Hologic WTA Tour career. 

"I played really good, I had a good start," Kalinskaya said. "I'm happy to be in the semifinals. I'm looking forward to it and I'm happy to have three matches [here], fourth one on grass, that gives me confidence for the longterm."

A finalist at the Dubai Duty Free Tennis Championships earlier in the season, Kalinskaya is now 7-0 against Top 10 players this season.