World tennis number one Serena Williams has marched into the semi-finals of the WTA Championships in Doha with a comfortable win over Elena Dementieva while sister Venus kept her title hopes alive.
Serena's straight sets victory completed a 100 percent record for the American in her group and confirmed her as the first player through to the last four at the season-ending tournament.
Venus, who suffered narrow defeats to Dementieva and Serena in her first two matches, beat Svetlana Kuznetsova and must now sweat on tomorrow's results before knowing whether she'll be involved in the play-offs.
Feisty teenager Caroline Wozniacki remains undefeated on her debut at the $6 million championships after beating Russian stand-in Vera Zvonareva in the other group.
Zvonareva, a replacement for fellow Russian Dinara Safina who withdrew with a back injury, was also in the wars, needing treatment in the second set as blood oozed from her nose.
The Russian later withdrew with an ankle injury meaning second reserve Agnieszka Radwanska of Poland will get a run out against semi-final hopeful Azarenka tomorrow.