DOHA (Reuters) - American Serena Williams will end the year as world number one for the first time since 2002 after Dinara Safina withdrew from the WTA Championships with a back injury on Wednesday.
Williams, who began the elite year-ending tournament 155 points behind the Russian in the rankings, won her opening match on Tuesday against Svetlana Kuznetsova, guaranteeing enough ranking points to overtake Safina even if she lost her remaining contests here.
With each victory in the round-robin phase at the $4.5 million tournament earning 230 points, Safina began her first group match against Jelena Jankovic 75 points adrift.
She earned 70 points just for taking to the court against Jankovic but was forced to retire after just two games clutching her lower back before announcing in a news conference that she would take no further part in the tournament.
Reporting by Martyn Herman; Editing by Ed Osmond