The Scotsman, who won the US Open last year, dropped the first set in his second-round win over Evgeny Donskoy. While he completed a straight-sets victory over Lu Yen-Hsun, he has rued allowing his opponent to take control of early points.
"I need to start games a bit better because I was letting him dictate a lot of points," Murray told BBC Radio Five Live. "He was able to change direction of the ball and that left me a bit flat-footed at some points.
"I felt a bit sluggish because he was so sharp, taking it so early at the beginning of the match but that improved as the match went on."
The 25-year-old will take on the lowest-ranked player remaining in the tournament, Carlos Berlocq, in the fourth round in California.