Sixth seed Lleyton Hewitt was given an easy passage into the last 16 of the U.S. Open when his Czech opponent Radek Stepanek retired injured while trailing 6-1 3-0 on Saturday.
Stepanek took a medical time out to receive treatment on an apparent back strain in the second set.
But since Hewitt was passing him with ease, Stepanek decided he could not continue.
Hewitt, champion at Flushing Meadows in 2001, faces Thai Paradorn Srichaphan for a place in the quarter-finals.