Azarenka digs deep to overcome Barthel

World number one Victoria Azarenka had to dig deep to overcome the hugely talented Mona Barthel of Germany 6-4, 6-7, 7-5 to reach the Stuttgart indoor tournament semifinals on Friday.

The Australian Open champion, who now faces Poland's Agnieszka Radwanska, won a hard-fought first set but had to fight off a sustained challenge from Barthel.

The German eliminated former world number one Ana Ivanovic and number seven Mario Bartoli of France in previous rounds.

Russian world number two Maria Sharapova needed three hours to get past Australia's Sam Stosur 6-7, 7-6, 7-5 and will now take on Wimbledon champion Petra Kvitova after the third-seeded Czech enjoyed a 6-4, 6-4 win over Germany's Angelique Kerber.

Earlier, fourth seed Radwanska recovered from a poor start to beat China's Li Na 3-6, 6-2, 6-3.

Nadal cruises

Top seed Rafa Nadal crushed Janko Tipsarevic 6-2, 6-2 in the last eight of the Barcelona Open on Friday to claim his semifinal place.

Canadian Raonic, who beat Andy Murray, set up a clash with third seed David Ferrer, who saved three match points in a 6-7, 7-6, 6-3 success against Spanish compatriot Feliciano Lopez.

World number two and holder Nadal, who is chasing a seventh Conde de Godo trophy in eight years, will face another Spaniard in 2010 winner Fernando Verdasco for a place in Sunday's final.

Verdasco went through in the last match of the day after Kei Nishikori of Japan was forced to retire with an abdominal injury when trailing 4-2 in the first set, an ATP spokesman said.