Injury setback for Nishikori
Third seed Kei Nishikori's hopes at the Delray Beach Open were ended by injury as he was forced to retire in his match with Teymuraz Gabashvili.
The Japanese player was 4-2 down in the first set to his Russian opponent when an injury to his left hip forced him to abandon the second-round match.
"I tried to play, but if you're not 100 per cent, it's tough," Nishikori said.
"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."
Next up for Gabashvili is a quarter-final meeting with seventh seed Marin Cilic after the Croatian swept aside American Ryan Harrison 6-3 6-4.
American John Isner, the second seed, had a tougher time of it against Dudi Sela, battling to a 3-6 6-1 7-6 (7-5) success.
"It puts a lot of stress on me playing matches like that. It seems I always do it but I'm glad to get through," said Isner.
"I wish I didn't have to dig so deep... I think he (Sela) may have got a little nervous (in the tiebreak)."
Rhyne Williams also needed three sets to progress, with the American overcoming Marcos Baghdatis 6-7 (9-7) 6-4 6-2.