Andy Murray overcame an ugly second set to beat Tim Smyczek 6-1 4-6 6-2 and book his place in the Farmers Classic quarter-finals.
Having received a bye in the first round, top seed Murray showed no signs of rustiness in his first competitive outing since Wimbledon as he raced through the first set in Los Angeles.
But his serve abandoned him in the second, before he composed himself in the third to seal the win and a last-eight tie against Colombia's Alejandro Falla, who beat fifth seed Ernests Gulbis earlier in the day.
Murray got off to the best possible start as he held then broke his American opponent to take a 2-0 lead.
And he kept up that pace to power through the first set without even facing a break point.
Things got tougher from there, however.
From nowhere, Smyczek fashioned three break points in game four of the second set and duly converted for a 3-1 lead.
Murray broke back immediately and held for 3-3, but the American did not roll over and again established a two-game lead at 5-3.
Again Murray broke back, but he simply could not buy a hold with his first-serve percentage for the set down at 42% and again surrendered to allow Smyczek to level the match.
The match continued in topsy-turvy fashion at the start of the third as the pair traded breaks in the opening two games.
Murray broke again for 2-1 and finally held to give himself a two-game cushion.
From there, he did not look back and broke again for a 5-2 lead before serving out for a win which he may consider was more difficult than it needed to be.
Murray, who split from coach Miles Maclagan this week, revealed he had struggled physically in his first match since losing to Rafael Nadal in the Wimbledon semi-finals a month ago.
The top seed said on the ATP World Tour website: "The first set was good and I started the second set with chances. I was struggling a little bit with my movement, when I got stiff and sore. But I managed to find a way to win.
"The top of my right hip and lower back was stiff. It isn't an injury, just on one of the changeovers my muscles started hurting. The last few changeovers I was standing up - something I have never done on tour before.
"There is a huge difference between the grass courts and hard."
Murray has never met Falla before on the main tour but he will be wary of the Colombian following his exploits at Wimbledon, where he served for the match against Roger Federer in the first round before eventually losing in five sets.
