Serena confirmed as number one for 2009

Dinara Safina was forced to withdraw from the season-ending Sony Ericsson Championships in Doha with a back injury last night, leaving Serena Williams to end 2009 as the world's number one - a feat the American celebrated with a defeat of her sister Venus.

The 23-year-old Russian was serving at 1-1 in the opening set against Serbia's Jelena Jankovic today when she had to retire.