Delray Beach, FL (SportsNetwork.com) - Last week's Memphis champion Kei Nishikori retired from his second-round match Thursday, while hot Croat Marin Cilic was an easy winner at the Delray Beach Open tennis event.

Russian Teymuraz Gabashvili was leading the third-seeded 2008 Delray Beach titlist Nishikori 4-2 in the first set when the Japanese star retired on Day 4, citing a nagging left oblique injury.

Second-seeded American John Isner had a scare in his match against Israeli Dudi Sela, dropping the first set before rallying for a 3-6, 6-1, 7-6 (7-5) victory.

Meanwhile, the seventh-seeded Cilic won for the 11th time in 12 matches by handling American wild card Ryan Harrison 6-3, 6-4 on the hardcourts at Delray Beach Tennis Center.

The former top-10 star Cilic titled in Zagreb in his native Croatia two weeks ago and was a runner-up in Rotterdam last week. He'll face Gabashvili in the quarterfinals on Friday.

The final match of the night saw American qualifier Rhyne Williams bounce back from a first set loss to take a 6-7 (7-9), 6-4, 6-2 victory over Cypriot wildcard Marcos Baghdatis.