DELRAY BEACH, Fla. -- John Isner held off an upset bid by Dudi Sela of Israel on Thursday night to advance to the quarterfinals of the Delray Beach Open after No. 3 seed Kei Nishikori of Japan exited the tournament because of a left hip injury.
The second-seeded Isner squandered four match points in the third set after leading 4-1, but the 6-foot-10 American rallied from a 5-2 deficit to prevail in the tiebreaker for a 3-6, 6-1, 7-6 (5) victory that earned him a spot in the quarterfinals for the third consecutive year.
"More times than not, when I'm up 4-1, I close it out," said Isner, who is 5-0 in his three-set matches this season but is playing in his first tournament since exiting the Australian Open with an ankle injury last month. "It definitely didn't need to go to 5-5 when I was up 4-1. I put a lot of stress on myself when I do that."
The world No. 13 will face American qualifier Rhyne Williams on Friday night. Williams ousted wild-card Marcos Baghdatis of Cyprus 6-7 (7), 6-4, 6-2 in Thursday's nightcap to reach his second ATP quarterfinal.
Nishikori's bid to win his second consecutive ATP title came to an abrupt halt Thursday afternoon when the top-ranked Asian was forced to retire during the first set of his second-round match because of a left hip flexor injury.
Nishikori was trailing Teymuraz Gabashvili of Russia 4-2 when he decided to stop the match. He said that he experienced discomfort for the first time during his first-round win Tuesday in which he stretched his win-loss record this season to 12-2.
"I tried to play, but if you're not 100 per cent, it's tough," said Nishikori, who is ranked No. 15 in the world and was coming off a win in Memphis last week. "I couldn't do anything today. It's going to take some time to recover. It's shocking this happened, especially since I've been playing well."
Gabashvili advanced to the quarterfinals on Friday and will face No. 7 seed Marin Cilic of Croatia, who defeated American wild-card Ryan Harrison 6-3, 6-4.
Samuel Groth and Max Mirnyi advanced to the doubles semifinals with a 7-6 (5), 6-4 win against Americans Sekou Bangoura and Vahid Mirzadeh. Harrison and fellow American Jack Sock filled out the final spot in the doubles semifinals with a 6-4, 7-5 win against Santiago Gonzalez and Scott Lipsky.