Atlanta: Mardy Fish opened his ATP Atlanta title defence on Thursday with a 6-3, 6-3 victory over France's Nicolas Mahut that put the top-seeded American into the quarter-finals.
Fish, who enjoyed a first-round bye, fired six aces and broke Mahut four times to finish off the second-round clash in less than 90 minutes.
Fish showed no ill effects from an abdominal muscle strain which had bothered him since the French Open.
The world number nine will play on Friday for a semi-final spot against Indian eighth seed Somdev Devvarman, who booked his first quarter-final since late April with a 6-1, 6-3 defeat of Japan's Tatsuma Ito.
Fish won four straight games in the second set before dropping his serve, immediately breaking back.
"That break-back was good, I was able to snatch the momentum," he said. "It was the first match back on outdoor hardcourt," added the 29-year-old.
"You always feel a bit of pressure coming back to place where you've had success.
"I'm happy just to move on, it's only going to get tougher from now on. The first match is always tricky. He's a tough opponent who serves well and plays aggressive."
Fish was joined in the last eight by 19-year-old compatriot Ryan Harrison, who waited out the evening weather delay to beat Belgian Xavier Malisse, the fourth seed, 6-7 (3/7), 6-4, 6-4.
The last few games were played after a thunderstorm halted play for nearly three hours.
Two-time grand slam winner Lleyton Hewitt, his ranking down to 174th, lost to Rajeev Ram of the United States 7-5, 2-6, 6-2. Ram, a qualifier, will line up against Harrison in the quarters.
Harrison said that he and Malisse exchanged choice words on a changeover after the weather delay, following back-to-back breaks of serve.
"When I broke him back he said some things that I wasn't too happy with. So I said some things back," he said.
"It was the heat of the moment. We both want to win. I like it when it gets intense, the competitive drive sparks me, it's an added motivation. But whoever wins will always get the last laugh."
The tournament is the ATP's first stop in the six-week US hardcourt build-up to the US Open, the final Grand Slam of the year that starts in New York on August 29.