John Isner was forced to retire from his match against David Nalbandian after landing awkwardly on his right ankle at the Cincinnati Masters. The 19th-ranked American was serving for the set, up 5-4, but down 0-30 in the 10th game.

The injury occurred on the first point during the ninth game, while Isner was up 5-3 in the first set.

Nalbandian held serve to go up 5-4, but pain forced Isner to call for a trainer again during the changeover. The American went back out to test the ankle, but to no avail. He foot-faulted on his first serve back, lost two points, and then retired from the match.

In the 4th round, Nalbandian will have his toughest opponent since his return, Novak Djokovic, the current world number three.