DUBAI, United Arab Emirates -- Former Wimbledon champion Petra Kvitova overpowered defending champion Agnieszka Radwanska 6-2, 6-4 Thursday to set up a semifinal against Caroline Wozniacki in the Dubai Championships.
Wozniacki, once ranked No. 1, defeated Marion Bartoli 4-6, 6-1, 6-4, capitalizing on 14 double-faults and 46 unforced errors by her opponent. Two double-faults cost Bartoli games in the second set.
Doubles specialist Roberta Vinci of Italy surprised former U.S. Open champ Sam Stosur 6-2, 6-4 in their quarterfinal. She will next face doubles partner Sara Errani, who downed Nadia Petrova of Russia 6-4, 0-6, 6-3.
Radwanska, ranked No. 4, had no answers for the big-hitting Kvitova, who neutralized her opponent with a powerful forehand.
"I think to beat Agnieszka here it means something more because she's defending champion, so she's playing well here," said Kvitova, who has a 4-1 record against the Pole. "So that's a good sign for me."
Kvitova had 38 unforced errors against Radwanska and said she would have to play better against Wozniacki.
"I am a player who is going for the winners, so I have to accept the unforced errors, too," she said. "I shoot bullets on the court next time."
Wozniacki was almost untouchable in the second set, and the third went back-and-fourth. Bartoli jumped ahead 2-0 and then Wozniacki ran off five straight games. Bartoli won two straight to make it 5-4, but Wozniacki was able to hang on and serve out the match.
Afterward, Diego Maradona, an ambassador for the Dubai Sports Council, came onto the court to give her one of his signed Argentina jerseys emblazoned with his No. 10. The Dane gave the soccer great a signed tennis racket.
"It was disappointing to lose that first set after I had been up," Wozniacki said. "But then I felt like she couldn't really do much in that second set because I was all over it."
Vinci put away Stosur, who lost in the quarterfinals in Doha last week following a second-round exit at her home Australian Open. Stosur made 28 unforced errors and was broken twice in each set.
"Way too many errors," Stosur said. "She did well to not be bothered by anything I was trying to do. She used her slice very well which kept all the points neutral."
Despite the latest setback, Stosur felt she was improving over her dismal start to the year.
"January didn't really go as well as I wanted it to. I wasn't playing up to the standard and level that I think I'm capable of," she said. "The last couple of weeks, it's gotten better. I've played many more good matches than bad."
Vinci also ousted sixth-ranked Angelique Kerber. Her coach told her to attack Stosur's backhand.
"She has an unbelievable forehand, so I tried to play against her backhand because she has a lot of problem with backhand, and try some slice and also some top when I have time," Vinci said.
Vinci said her success in doubles -- the Italian has 19 doubles titles to only seven singles -- has contributed to her resurgence in singles, where she was ranked 17th.
"In doubles, you can try something that you can play in singles," she said. "I probably play more relaxed and then I play better in the singles."