By Larry Fine

NEW YORK (Reuters) - Twice grand slam winner Stan Wawrinka rallied from 5-2 down in the second set to clinch victory over Italian Alessandro Giannessi on Thursday and reach the third round of the U.S. Open.

After dominating the opening set, the third-seeded Swiss battled back to force a tie break and then broke the Italian in the final game of the match to finish a 6-1 7-6(4) 7-5 victory.

"I was trying to be a little more aggressive," said Wawrinka, who blasted 57 winners, including 26 off his forehand.

"I'm very happy the way I won the match."

Wawrinka will now face either Germany's 27th seed Alexander Zverev or unseeded Briton Daniel Evans.

(Editing by Greg Stutchbury)