Defending champion Sam Querrey and Brit Kyle Edmund eased into the Delray Beach Open second round on Monday.
Querrey, winner of the ATP 250 event in Florida last year, led Dudi Sela 6-2 2-1 when the Israeli retired.
The fourth-seeded American wildcard had broken three times before Sela, who had won two of their previous four meetings, called it quits.
The only other seed in action was Edmund, who crushed Frenchman Adrian Mannarino 6-3 6-0.
Talented American teenager Taylor Fritz brushed past qualifier Akira Santillan 6-4 6-4 and Yoshihito Nishioka beat Kimmer Coppejans 6-3 6-3.
The day's only three-setter saw Lu Yen-hsun battle past wildcard Bjorn Fratangelo 4-6 7-5 6-4.