ISTANBUL - Australia's Samantha Stosur destroyed China's Li Na 6-1 6-0 in little more than an hour to reach the semi-finals of the WTA Championships for the second consecutive year on Friday.

Samantha Stosur of Australia celebrates her victory against Li Na of China after their WTA tennis championships match in Istanbul, October 28, 2011. [Photo/Agencies]

Their final White Group round-robin clash had effectively become a decider to see which of the year's surprise grand slam champions would progress along with Victoria Azarenka but the match proved embarrassingly one-sided.

U.S. Open champion Stosur had far too much firepower for the listless 29-year-old as she romped to victory in front of a large crowd in the Sinan Erdem Arena.

She has now won all six career meetings against the French Open champion, dropping just one set in the process.

Azarenka, who has already won the group after crushing victories over both Stosur and Li, completes the group phase later against alternate Marion Bartoli who will get one match in the big-money event after Maria Sharapova's withdrawal.

Before that the final Red Group match features already-qualified Petra Kvitova of the Czech Republic and Poland's Agnieszka Radwanska.

Radwanska, the world number eight and the final player to qualify for the tournament's Istanbul debut, needs just a set to claim the runners-up spot in the group ahead of Russia's Vera Zvonareva who she beat on Thursday having saved three match points.

The winner of the match will top the group and play Stosur in the semi-finals.