Andy Roddick has revealed that he was suffering from nerves ahead of his victory over Bernard Tomic in the second round of the US Open on Friday.

The American, who defeated the Australian in straight sets, announced earlier this week that he would be retiring when his run at the tournament ends.

"I had no idea what was going to happen out there, honestly, even before the match," Roddick said. "I've played a lot of matches and that was a different kind of nerves than I've had before.

"That was surprising for me. I felt weird before the match. Twenty minutes before it was kind of getting the best of me. I had to get my stuff together before I walked out there."

Roddick's next opponent is Italian world number 59 Fabio Fognini.