Roger Federer's record four and a half year reign as world men's tennis number one could end this week after he was beaten in the third round of the Cincinnati Masters.
The Swiss went down in three sets to Croatia's Ivo Karlovic.
The defeat by the big-serving Karlovic was Federer's 11th loss of the season and his first against his opponent in seven matches.
World number two Rafael Nadal of Spain, who beat Federer in this year's Paris and Wimbledon finals, will take over from the Swiss as the world's top-ranked player if he wins the tournament.
