STUTTGART, Germany - The two hottest players of the year will square off in the semifinals of the Porsche Tennis Grand Prix, after Victoria Azarenka and Agnieszka Radwanska scored quarterfinal victories on Friday.

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The No.4-seeded Radwanska won first, battling from a set and a break down to beat No.8 seed and reigning French Open champion Li Na, 36 62 63.

"She was playing very well today, and I think I wanted to do too much in the beginning," Radwanska said. "I was making a couple of mistakes early but in the second set I knew I had to be more calm and serve much better. It was very close and I'm happy I could turn it around and beat her on clay courts."

The No.1-seeded Azarenka followed Radwanska into the semifinals, but not until almost three hours later - having led 64 31 and seemingly closing in on a straight set victory, Azarenka ended up having to battle for two hours and 48 minutes to finally get by German wildcard Mona Barthel, 64 67(3) 75.

"I felt like she was playing much better when she was down," Azarenka said afterwards. "She would go for her shots and it seemed like everything would go in - but I fought hard and tried to just stick with her, and if I couldn't take one opportunity, I'd try to take the next one - I knew I'd get another one."

Barthel had her chances, going up a break early in the third set, and she served big - she had 13 aces in the match. But she also had 16 double faults in the match, including two in the final game, and one on the final point.

"Mona has been showing some excellent tennis throughout the year," Azarenka said. "She has a big serve and big strokes, and she's just coming up, so she has absolutely nothing to lose - it's no surprise she's going to come out and show great tennis. She already had two good wins here in Stuttgart."

Azarenka leads Radwanska in their head-to-head series, 9-3, but the takeaway stat from that is Azarenka is 4-0 against her this year, coming back from a set down to win in the semifinals of Sydney and quarterfinals of the Australian Open, then scoring straight set wins in the semifinals of Doha and quarterfinals of Indian Wells - the Indian Wells scoreline was 60 62.

"We've played each other many times, especially this year - the fifth time this year now," Radwanska said. "It's kind of weird, but we have no choice!"

Aside from a berth in the final, there's another thing at stake - Azarenka and Radwanska are this year's match win leaders so far, both at 28 right now, so whoever wins on Saturday will be the standalone match win leader for the year. Azarenka is 28-1 (the only loss coming to Marion Bartoli in Miami) and Radwanska is 28-4 (all four of those losses coming to Azarenka).