American Serena Williams reached the semi-finals at the WTA Tour Championships in Istanbul on Thursday with what is fast becoming a routine defeat of world number one Victoria Azarenka.
The Wimbledon and U.S Open champion recorded a 6-4 6-4 win at the season-ending event, her fifth triumph over the Belarusian this year. Williams also owns an 11-1 record in their career head-to-heads.