Serena Williams wins third WTA Tour Championships crown

Serena Williams has won the WTA Tour Championships for a third time with a straight-sets victory over Maria Sharapova in Istanbul.

The 31-year-old American, who didn't drop a set during the whole tournament, saw off the Russian world number two 6-4 6-3.

The win has capped a fine year for Williams following victories at Wimbledon and the US Open as well as gold medals in both the singles and women's doubles at the London Olympics.

A ninth career victory over Sharapova has seen Williams end the year as the world number three.