Serena Williams stayed on course to end the year as world number one when she beat Russia’s Svetlana Kuznetsova 7-6, 7-5 on the opening day of the WTA Championships .

Second-ranked Serena, who must better Dinara Safina’s performance here to snatch the No.1 spot, served 11 aces under the Khalifa Stadium floodlights to get the better of the French Open champion who led 6-4 in the first-set tiebreak.

She will play Venus in her second round-robin match on Wednesday knowing that victory would almost certainly eliminate her older sibling.

In the opening match in White Group, former world number one Jelena Jankovic lost 6-2, 6-3 to tournament debutant Victoria Azarenka of Belarus. World number one Safina begins her tournament against Jankovic on Wednesday while Azarenka plays Denmark’s Caroline Wozniacki.

Eleven-times grand slam champion Serena, bidding to end the year top of the WTA rankings for the first time since 2002, was far from her best in a scrappy slug-fest against Kuznetsova.

With the match starting around 10pm local time, only a sprinkling of fans remained in the 7,000-seater Centre Court and the subdued atmosphere appeared to affect both players as they regularly found the net in high humidity.

Kuznetsova looked poised to win the opening set when she came back from 1-3 down in the tiebreak to lead 6-4 but a Williams winner and an ace helped the American snuff out the danger and she won the next two points to move ahead.

“At that point I thought I had ruined it for myself because I missed an easy shot to go 4-1 up in the breaker,” Williams, who needed treatment on her ankle in the second set, told reporters.

World number three Kuznetsova, yet to survive the round-robin stage in four appearances at the Championships, gifted Serena a break of serve at 5-5 in a tight second set with a double-fault, effectively sealing her fate.