Maria Sharapova of Russia returns a shot to Agnieszka Radwanska of Poland during their quarterfinal match at the WTA Istanbul Cup tennis tournament in Istanbul May 24, 2007.[Reuters]

Number one seed Maria Sharapova was made to work hard before securing her semi-final place at the Istanbul Cup with a 6-2 3-6 6-0 defeat of Poland's Agnieszka Radwanska on Thursday.

The Russian will play Aravane Rezai in the last four after the unseeded Frenchwoman put out American Meghann Shaughnessy 1-6 6-1 6-4.

Second-seed Elena Dementieva also needed three sets to overcome Colombian Catalina Castano, winning 6-1 4-6 6-4.

The Russian had said at the start of this month she had considered retirement after suffering a stress fracture of three ribs while working with a new physical trainer in Moscow.

Dementieva next takes on Ukrainian fifth seed Alona Bondarenko, who enjoyed a bye into the last four after Swiss Patty Schnyder withdrew because of a quadriceps injury