( 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 was n'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 . 7 seed Sara Errani . Samantha Stosur into quarterfinals at the last eight in France .