Australian Matthew Ebden struck 20 aces as he defeated well-performed American James Blake to reach the quarter-finals of the ATP Tour's Atlanta Open.
World No.82 Ebden, who won 88 per cent of his first serve points, claimed the decisive break in the ninth game of the third set in a 6-7 (8-6) 6-4 6-4 second round victory.
He will play his first quarter-final since last October at the Shanghai Masters when he faces Luxembourg's Gilles Muller in the last eight.
Muller advanced after second seed and two-time reigning champion Mardy Fish was forced to retire from their match midway through the second set.
Fish led Muller 6-4 2-2 before rolling his left ankle trying to chase down a drop shot, falling to the ground and staying down for about a minute.
He got up and limped off to his sideline chair, sat down for a short break and returned to finish the fifth game but then chose to withdraw.
Fish, who beat American compatriot John Isner in the last two Atlanta finals, recently underwent a procedure called cardiac catheter ablation, which deals with misfiring electrical pulses in the heart.
Isner, meanwhile, advanced to the quarter-finals by defeating Ruben Bemelmans of Belgium 4-6 6-3 6-4.
American Jack Sock also won his second round match by beating Steve Johnson 7-6 (7-5) 7-6 (7-5).