NEW YORK (Reuters) - Former champion Marin Cilic of Croatia retired from his first-round match against German Philipp Kohlschreiber on Monday with an apparent injury, his earliest exit from the U.S. Open in 13 attempts.

The 2014 winner had been up two sets but bowed out of the match early on in the fifth with Kohlschreiber leading 2-0, after struggling with his serve.