Serena Williams becomes oldest world number one

Serena Williams has become the oldest player to top the WTA rankings with victory over Petra Kvitova in the quarter-finals of the Doha Open.

The 31-year-old American needed to reach at least the semi-finals of the tournament to oust Victoria Azarenka as the best player in the world.

Williams saw off former Wimbledon champion Kvitova 3-6 6-3 7-5 to make it through to the last four, where she will meet Maria Sharapova.

Williams last sat atop the world rankings in November 2009 before she was replaced by Caroline Wozniacki in October 2010.