Roberta Vinci beats No . 7 seed Samantha Stosur at Dubai Championships . 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 . Unseeded Italian will now play doubles partner and ' sister ' Sara Errani . Petra Koch knocks out No . 2 seed Marta Radwanska . Juan Martin Del Porto into quarterfinals at Open 13 in Marseille .
Roberta Vinci beats No . 7 seed Samantha Stosur at Dubai Championships . Unseeded Italian will now play doubles partner and ' sister ' Sara Errani . Petra Koch knocks out No . 2 seed Marta Radwanska . Juan Martin Del Porto into quarterfinals at Open 13 in Marseille .