Top-seeded American Mardy Fish shook off a sluggish start to beat Gilles Muller 7-6 (7/1), 6-1 on Thursday and reach the quarter-finals of the $619,500 ATP Los Angeles hardcourt tournament.
Fish, ranked ninth in the world, was playing his first match since winning his sixth career title with a victory over John Isner in the Atlanta final on Sunday.
"I came out a tad flat," said Fish, who dropped his serve in the second game and said his ability to immediately break back was the key.
The first set went with serve from there, and Fish built momentum heading into the tiebreaker when he closed out the 12th game with two straight aces.
Once he had sped through the tiebreaker, Muller offered little resistance.
"He's a guy that plays very well ahead, or equal," Fish said. "Getting up a set, I knew he was going to be upset after playing a pretty good first set and losing it."
In the second set, Fish took a 3-0 lead then broke Muller for a 5-1 lead, advancing in the next game on his second match point when Muller sent a forehand wide.
In Friday's quarter-finals Fish will face eighth-seeded Igor Kunitsyn of Russia.
Kunitsyn defeated tenacious American Ryan Sweeting 7-6 (7/4), 7-6 (8/6).
After Sweeting saved one match point in the tiebreaker, Kunitsyn set up another with an angled forehand volley for 7-6, sealing the victory just as the match clock ticked past two hours.
Fourth-seeded Brazilian Thomaz Bellucci roared into the quarter-finals downing Colombia's Alejandro Falla 6-0, 6-1 in 51 minutes.
Like Fish, Bellucci enjoyed a first-round bye. But the 34th-ranked Brazilian wasted no time, winning the opening set of the second-round match in 28 minutes.
Falla won the first game of the second set, but Bellucci then re-asserted himself to wrap up the contest between two South American left-handers who are playing doubles together here.
Bellucci next faces American Alex Bogomolov, who upset seventh-seeded Bulgarian Grigor Dimitrov of Bulgaria 6-4, 6-3.
Friday's other two quarter-finals were set on Wednesday.
Second-seeded Argentinian Juan Martin del Potro will take on Latvia's Ernests Gulbis and 19-year-old American Ryan Harrison will play Taiwan's Lu Yen-Hsun.
Del Potro, the 2009 US Open champion, won the title in Los Angeles in 2008.