DOHA: Russia’s Dinara Safina hobbled out of the WTA Championships on Wednesday, surrendering the year-end World No 1 ranking to Serena Williams in the process.

Williams then celebrated the landmark by beating sister Venus 5-7, 6-4, 7-6 (7/4), sending the defending champion to a second defeat and virtually certain of exiting the $4.55m event. Safina quit her opening match against Jelena Jankovic with a lower back injury with the score at 1-1 in the first set and after only 13 minutes on court. Safina had gone back to the top of the rankings on Monday, but only with a 155-point lead on Williams.

The American won her opener on Tuesday against Svetlana Kuznetsova, and then added more points by beating Venus. Organisers said fellow Russian Vera Zvonareva, the 2008 runner-up, would take Safina’s place in the competition.

Safina said she had started feeling the inflammation on her way to her third title of 2009 in Portoroz in July, but had been determined to keep playing to stay on course for the year-end top spot. Safina added that she will have to make a decision on whether or not to skip the 2010 Australian Open in order to complete her recovery.