Mahesh Bhupathi and Mark Knowles advanced to the semi-final of the Cincinnati Masters with a narrow win over American wild card duo of Mardy Fish and John Isner.

Bhupathi-Knowles, the No.4 seeds, defeated the American pair 7-5, 6-7(5), 12-10 in the quartfinals on Thursday.

Fish and Isner (pictured) upset fifth seeds Jonas Bjorkman and Kevin Ullyett 7-6(4), 7-6(14) in their second round match, but then came up short against the Indo-Bahaman duo.

Bhupathi and Knowles advance to the semifinals for the first time since April at Masters Series Monte-Carlo, where they finished runners-up to Rafael Nadal and Tommy Robredo. They will face the top seeds Mike and Bob Bryan in the semis on Saturday.