(CNN) -- Unseeded Italian Roberta Vinci prolonged the best week of her career to date by dumping No. 7 seed Samantha Stosur out of the Dubai Tennis Championships to take her place in the last four. But her second scalp of the week has set up an uncomfortable semifinal, against best friend Sara Errani, who also happens to be the doubles partner she's claimed three grand slam titles alongside. Having disposed of Angelique Kerber in the third round on Wednesday, Vinci was in solid form again as she took just an hour and 18 minutes to beat her Australian opponent 6-2 6-4. Errani, the No.5 seed Sara, disposed of Russia's Nadia Petrova 6-4 0-6 6-3 to set up a clash that will bring forward mixed emotions for both players. "It will be different mentally because I know her, she's like a sister for me and we play doubles together all the time," Errani told the Tour's official website. "Normally she's with me on my side of the net and not on the other one, so to see her on the other side is tough because one of us will lose. "She's an amazing person outside the court. Outside the court she will always try to help you when she can. She's like a sister to me. We stay together maybe 300 days a year. Of course we have had a lot of good moments together. "I will have to think about it as just another tennis match, and not that it's against her. I just have to go on the court and do my best. The good thing is one of us will be in the finals here." Elsewhere, Agnieszka Radwanska, the No. 3 seed from Poland, was knocked out by Petra Kvitova who grabbed her first win over a top five player since the 2011 season. Czech Kvitova hit 37 winners compared to Radwanska's six and will now face Caroline Wozniacki in the semis. The Dane edged a grueling match with Marion Bartoli, of France, to win 4-6 6-1 6-4. "It was disappointing to lose that first set after I had been up; I'm happy I turned it around," Wozniacki said. "In the third set I was down 2-0 and it could have been 3-0, and all of a sudden it wasn't looking good, but I kept fighting and every game was close, and I'm happy I ended up winning it." At the Open 13 tournament in Marseille, Juan Martin Del Potro, the No. 2 seed from Argentina, moved into the last eight after beating France's Michael Llodra 3-6 7-6 7-5. Del Potro, the 2009 U.S. Open champion will face another home favorite in the next round, Gilles Simon, after he beat Spain's Roberto Bautista Agut 6-3 6-1. Russia's Dmitry Tursunov is also into the last eight after toppling fourth seed Janko Tipsarevic, of the Czech Republic, 7-6 6-2.
Roberta Vinci beats No. 7 seed Samantha Stosur at Dubai Championships .
Unseeded Italian will now play doubles partner and 'sister' Sara Errani .
Petra Kvitova knocks out No. 3 seed Agnieszka Radwanska .
Juan Martin Del Porto into quarterfinals at Open 13 in Marseille .
(CNN) -- Unseeded Italian Roberta Vinci prolonged the best week of her career to date by dumping No. 7 seed Samantha Stosur out of the Dubai Tennis Championships to take her place in the last four. But her second scalp of the week has set up an uncomfortable semifinal, against best friend Sara Errani, who also happens to be the doubles partner she's claimed three grand slam titles alongside. Having disposed of Angelique Kerber in the third round on Wednesday, Vinci was in solid form again as she took just an hour and 18 minutes to beat her Australian opponent 6-2 6-4. Errani, the No.5 seed Sara, disposed of Russia's Nadia Petrova 6-4 0-6 6-3 to set up a clash that will bring forward mixed emotions for both players. "It will be different mentally because I know her, she's like a sister for me and we play doubles together all the time," Errani told the Tour's official website. "Normally she's with me on my side of the net and not on the other one, so to see her on the other side is tough because one of us will lose. "She's an amazing person outside the court. Outside the court she will always try to help you when she can. She's like a sister to me. We stay together maybe 300 days a year. Of course we have had a lot of good moments together. "I will have to think about it as just another tennis match, and not that it's against her. I just have to go on the court and do my best. The good thing is one of us will be in the finals here." Elsewhere, Agnieszka Radwanska, the No. 3 seed from Poland, was knocked out by Petra Kvitova who grabbed her first win over a top five player since the 2011 season. Czech Kvitova hit 37 winners compared to Radwanska's six and will now face Caroline Wozniacki in the semis. The Dane edged a grueling match with Marion Bartoli, of France, to win 4-6 6-1 6-4. "It was disappointing to lose that first set after I had been up; I'm happy I turned it around," Wozniacki said. "In the third set I was down 2-0 and it could have been 3-0, and all of a sudden it wasn't looking good, but I kept fighting and every game was close, and I'm happy I ended up winning it." At the Open 13 tournament in Marseille, Juan Martin Del Potro, the No. 2 seed from Argentina, moved into the last eight after beating France's Michael Llodra 3-6 7-6 7-5. Del Potro, the 2009 U.S. Open champion will face another home favorite in the next round, Gilles Simon, after he beat Spain's Roberto Bautista Agut 6-3 6-1. Russia's Dmitry Tursunov is also into the last eight after toppling fourth seed Janko Tipsarevic, of the Czech Republic, 7-6 6-2.
(CNN) -- Unseeded Italian Roberta Vinci prolonged No. 7 seed Samantha Stosur out of the Dubai Agnieszka Radwanska, the No. 3 seed from Poland, Radwanska's six and will now face Caroline in Marseille, Juan Martin Del Potro, the No. 2