Dubai –Roberta Vinci and Sara Errani, the world's top doubles pair, will put their lifelong friendship to one side on Friday when they clash in the semifinals of the $2 million Dubai Open.

Vinci, who had accounted for one former Grand Slam winner and one seeded player already, beat the seventh-seeded former US Open champion, Samantha Stosur 6-2, 6-4 to reach the last four on Thursday.

Errani, who had played one long three-set match already, had another, beating Nadia Petrova, the former world number three from Russia, 6-4, 0-6, 6-3, to reach the semi-finals.

The unseeded Vinci's steadiness and mixtures of pace and spin teased too many errors from Stosur, who came back from 3-5 down to within sight of 5-5 in the second set but never played with enough conviction to suggest she could win.

The doubles experts now both have a tougher struggle, as they have to turn a relationship in which they breakfast, practise and train together, into one in which they temporarily regard each other as an obstacle to be overcome.

Vinci said it would be like “playing my sister,” and Errani pointed out how strange it might feel as they spend about 300 days together during the year.

“I'm number one in the world in doubles, so it's incredible for me,” said Vinci who is ranked 17 in singles.

“I'm probably playing singles in a more relaxed way, and so I'm playing better.”

She added: “It was a great match for me, great performance. I played a good game today like yesterday,” she said, referring to her straight sets win over Angelique Kerber, the fourth seed from Germany.

Errani worked like a trojan from the back of the court against the more powerful and more unpredictable game of Petrova, and prevailed after two and a half hours and the expenditure of much energy.

“I tried to recharge my batteries after losing that second set, and also to show her that I was not tired,” the fifth seeded Italian said.

With Victoria Azarenka and Serena Williams, the world number one, both withdrawing belatedly, the tournament has become much more wide open, making it a particularly good time for the Italians to have decided to take a rest from doubles.

Defending champion, Agnieszka Radwanska, the world number four from Poland, and Petra Kvitova, the former Wimbledon champion from the Czech Republic, were facing off in one of the other quarter-finals.

Caroline Wozniacki, the former world number one from Denmark, was to face Marion Bartoli, the former Wimbledon finalist from France, in the other. – Sapa-AFP