LINZ, Austria - Top seeds Aryna Sabalenka and Elise Mertens each moved into the semifinals at the Upper Austria Ladies Linz to complete quarterfinal action on Friday. Mertens was first through as the Belgian dispatched No.5 seed Veronika Kudermetova, 6-4, 6-1, while Sabalenka led Oceane Dodin, 6-3, 3-3 when the French qualifier was forced to retire due to an ankle injury.

Mertens was fresh off a tough three-set win over former World No.2 Vera Zvonareva in the second round, but made much quicker work of Kudermetova to advance after 92 minutes on Centre Court.

"I slept in a little bit longer to get an extra hour, but I managed the turnaround pretty well after a slower start," she said after the match. "From there, I played much better."

Still, the two-time US Open quarterfinalist didn't have things all her own way as the young Russian broke to open the match and was two points from a 4-1 lead before Mertens got a foothold in the match, winning five of the next six games to sweep the opening set.

"I tried to keep putting that one more ball in because she's a hard hitter. She has great groundstrokes but can also make mistakes so as aggressively as I tried to play, I also wanted to allow her to make that mistake."

Carrying that momentum into the second set, the No.2 seed raced ahead 5-1 and edged through a tense final game to convert her third match point opportunity.

"The bounce here is a little lower, so it's so important to accelerate enough to get the ball over the net, instead of into it! I'm trying not to hit too flat here, so it's been good to change the rhythm. Most of all, you need to have confidence in your shots to hit the higher ball."

Standing between the former Australian Open semifinalist and a second final in 2020 is No.4 seed Ekaterina Alexandrova, who bounced French Open semifinalist Nadia Podoroska in two quick sets earlier in the afternoon.

"I'm ready to go. I'm doing everything I need to do after a good match: getting the good night's sleep, warming up and seeing the physio. It's the last tournament of the year so I'll give everything I have."

Following Mertens was longtime doubles partner Sabalenka, who is closing in on a first-ever season-ending Top 10 finish should she reach the final. Taking on Dodin in a rematch of their US Open first round from a few weeks ago, the big hitters traded body blows from the baseline and an early exchange of breaks to start the match.

"From the US Open, I remember how well she serves, and I also remembered some of her favorite spots to serve," Sabalenka said. "She hits so flat and deep, so I was going to have to be really quick with my feet and stay low. I practiced a lot of that with my coach, but even still, it was a tough match because she was playing really well. She made a lot of crazy winners, so I'm sorry that she hurt her ankle. I hope she gets better soon."

The Belarusian soon found the level that had already won her six straight matches - having won the J&T Banka Ostrava Open last month - and scored a crucial break to serve out the opening set.

Things remained close in the second set before a wrong-footed Dodin injured her right ankle, leading to an immediate end to the match.

"This isn't how I wanted to finish the match, but I'm still happy I was able to win the first set and win every game in the second."

Sabalenka will next face rising Czech star Barbora Krejcikova, who opened play on Friday with a straightforward win over Aliaksandra Sasnovich.

"I've played against her in doubles before, and those have always been tough matches. She serves and plays very well, and she's moving especially well; she seems to be in that shape you need to be in for singles. I'll watch some of her matches today and figure out some tips with my coach."

Linz 2020 highlights: Alexandrova ousts Podoroska