Top seeded American Andy Roddick [Images] was forced to default his semi-final match against Denmark's Kenneth Carlsen because of an ankle injury at the Kroger St Jude ATP event in Memphis on Saturday.

The world number three, who was bidding for his second consecutive ATP title, withdrew after injuring his left ankle, officials said.

Roddick told The Commercial Appeal of Memphis he sprained his ankle in the second set of his quarter-final match with Robby Ginepri on Friday.

"At three-all ... in the second set, I turned it pretty good," Roddick said. "At first it wasn't too bad but, by the end, it was definitely noticeable."

Roddick said he was concerned about risking further injury before next month's Davis Cup match against Croatia in Carson, California.

"Let's be honest, I have Davis Cup around the corner," he said of the March 4-6 tie.

"That's obviously a part of my season, and I have to think of my team mates as well in that aspect."

Denmark's Carlsen will face Max Mirnyi of Belarus in Sunday's final. Eighth-seeded Mirnyi upset second-seeded Tommy Haas 7-5 6-3 in the day's other semi-final.

In the WTA event, top-seeded Russian Vera Zvonareva successfully defended her title with a 7-6, 6-2 win over third-seeded American Meghann Shaughnessy.

The victory was the third WTA career title for the 20-year-old Russian.

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