Russia's Maria Sharapova reacts during her quarterfinal match against Poland's top seed Agnieszka Radwanska at the Porsche tennis Grand Prix in Stuttgar. Picture: dpa, Daniel Maurer

Stuttgart, Germany -

Defending champion Maria Sharapova marched into the semi-finals of Stuttgart's WTA tournament with a 6-4, 6-3 win over top-seed Agnieszka Radwanska on Friday.

“That was a big win for me,” admitted Sharapova after picking up her 11th straight win in Stuttgart where she is bidding for a hat-trick of titles having won the 2012 and 2013 tournaments.

“That was my biggest win since my comeback from injury,” she added having missed four months last year with a shoulder injury.

Sharapova claimed her ninth win in 11 matches against world number three Radwanska of Poland, but the Russian did not have things her own way in her one hour, 39 minute victory.

After a total of seven breaks at the start of the match, as the momentum swung back and forth, Sharapova finally won her first service game to take control of the first set.

“That was one of the key moments,” she said after eventually needing eight match points to claim the win.

She will now face Sara Errani in Saturday's semi-final after the Italian's quarter-final opponent Carla Suarez Navarro of Spain was forced to retire injured in the third set with Errani leading 6-3, 6-7 (6/8), 3-0.

“It'll be a tough game, she's a clay-court specialist,” said the Russian.

Having won all four Grand Slam titles, Sharapova is bidding to claim a personal landmark this week in Stuttgart by winning a tournament three times in succession.

Victory bought an extra bonus for the Russian as failure to beat Radwanska would have seen her fall out of the top ten for the first time in three years.

Ana Ivanovic of Serbia clinched a 6-3, 2-6, 6-4 quarter-final win over Russia's Svetlana Kuznetsova.

Ninth-seed Ivanovic will play former world number one and compatriot Jelena Jankovic for a place in Sunday's final after the latter's 6-4, 6-3 quarter-final win over Russia's Alisa Kleybanova. - Sapa-AFP