(Reuters) - Defending champion Serena Williams reached the semi-finals of the Western & Southern tournament in Cincinnati but not before having her mettle tested in a 3-6 6-4 6-2 win over sixth-seeded Serb Ana Ivanovic on Friday.
Williams, who will be chasing a calendar sweep of the four grand slams at the Aug. 31-Sept. 13 U.S. Open, struggled with her serve and was forced to come from behind several times in a rematch of last year's final.
"Out of the previous nine times we've played I think we've gone three sets at least six times so I know she plays really well," the top-seeded American said in an on-court interview.