Azarenka made to toil

Victoria Azarenka moved a step closer to securing the year-end number one ranking with a 6-7, 7-6, 6-4 win over Germany's Angelique Kerber at the WTA Championships on Wednesday.

Azarenka needed three hours and six minutes to repel Kerber but Maria Sharapova's 5-7, 7-5, 7-5 win over Agnieszka Radwanska took even longer to complete, the three hours and 12 minutes contest ending at 02:12 local time on Thursday morning.

In another tight contest that opened the evening session, number three Serena Williams took down China's Li Na 7-6, 6-3 in one hour and 50 minutes.

With her round robin victory in the Red Group, Azarenka only needs to win one more match to secure the year-end top spot. With their second wins of the Championships, Sharapova and Williams both guaranteed themselves spots in the semifinals.

Belarusian Azarenka fought off two match points at 6-5 down in the second set in brilliant fashion before posting a fien win.