Madrid: World No. 1 Justine Henin began the defence of her WTA Championships singles title with a confident 6-1, 7-6 win over Russian Anna Chakvetadze on Tuesday.

The 25-year-old Belgian rattled through the first set in 24 minutes but had to resist a determined fight-back by her opponent before winning her opening round-robin match in the yellow group of the $3 million end-of-season tournament.

Ana Ivanovic, the youngest of the eight players in Madrid, celebrated her 20th birthday with a 6-1, 4-6, 7-5 victory over world No. 2 Svetlana Kuznetsova in an enthralling encounter in the Red Group.

Ivanovic blew Kuznetsova away in the first set but the gritty Russian levelled and the two players produced outstanding tennis as they slugged it out in the decider, the Serb eventually edging the win with a break in the final game.

Maria Sharapova, who won the event on her debut appearance in 2004 but has struggled with injury problems this season, also made a winning start in the Red Group with a 6-4, 7-5 victory over Daniela Hantuchova.

Sharapova looked on course for a straightforward win after dominating the first set, but Hantuchova refused to go down without a fight and saved four match points.