Anett Kontaveit scored her first tour-level win against Ons Jabeur at the Sydney Tennis Classic on Thursday, but not in the way she might've hoped.

The No.4 seed secured a semifinal berth when Jabeur, seeded No.7, retired with a low back injury after losing the opener, 6-4.

After nearly an hour on court, Jabeur received a medical timeout after the set was completed, and attempted to start the second set: after serving a let and a first-serve fault, the Tunisian walked to the net for a match-ending hug. 

"I really hope that Ons is going to be fine for next week and that it's nothing too serious," Kontaveit said. "The first set was really competitive and we've had some tough matches before, but she's always come on top. I was really happy to get the set and that I was playing the way I was playing." 

Kontaveit lost to Jabeur twice last season, but Thursday's meeting Down Under was the pair's first since the were two of the main characters of the season-ending story where Kontaveit eclipsed Jabeur for the eight and final spot at the Akron WTA Finals in Guadalajara. In the 51-minute set, Kontaveit won the last three games en route to the abridged victory. 

Another rematch up next: With eyes on a fourth straight final, she advances to a semifinal against No.3 seed Barbora Krejcikova, who eased to a 6-0, 6-2 win over France's Caroline Garcia. The pair played just two months ago in Guadalajara, where Kontaveit swept to a 6-3, 6-4 win in the round-robin.

"It's definitely going to be a tough match. She's playing great. She's had good wins," Kontaveit said. "The season is so early on. Last time we played was the end of the season. It was different conditions, of course.

"I'm really looking forward to the challenge to play another Top 10 player. I'm glad to be putting myself in these situations and getting good matches and getting quality time on court."

Kontaveit's single set was nearly as long as Krejcikova's completed victory, as the reigning French Open champion needed just 68 minutes to advance past Garcia and into the final four.

Sydney: Krejcikova sweeps past Garcia into semifinals

The World No.4 has dropped just eight games in two victories in her Sydney singles debut, and won eight games in a row to start the match against Garcia. The Frenchwoman gained some ground in the second set, where she had a break point for 3-3, but also lost the last three games of the match. 

"I was feeling very well today and I'm really enjoying the atmosphere here and the beautiful stadium. I'm looking forward to playing another one soon," Krejcikova said on-court in victory. 

"Anett, she's playing very well. She was playing well last year, she's playing well this year again. She's continuing her beautiful streak so I'm really looking forward to see where my level is and to play against her. It's going to be a nice match."