Murray is ranked 60 in the world

The 18-year-old Scot swept past Fish 6-2 6-2 and goes on to face another American, James Blake, or Taipei's Yeu-Tzuoo Wang.

Murray fired down five aces and was broken only once, while he converted six of his 11 break-point chances.

"That's the best match I've played this year so far. I feel like I'm hitting well and I was moving well," he said.

"I've been struggling with my serve but I've practised a lot in the last couple of weeks and I was happy with my serve tonight."

Murray is looking to get his season moving after coming into the tournament with two wins and four defeats in 2006.

Tim (Henman) understands so much about the game that he can give advice on anything Andy Murray

The victory also avenged a three-set defeat in his only previous match against Fish in Indianapolis last year.

"Since I played him last year, this time I knew his strengths and weaknesses and it helped me get my position early in the rally.

"I was aggressive on the right balls and I was taking risks and I played a really solid match. I'm really happy with how it went."

An impressive performance from Murray - hopefully he'll keep this form going From TR Have your say on Five Live

Murray also revealed that after his first-round exit to Juan Ignacio Chela at the Australian Open, he sat down with coach Mark Petchey and British number one Tim Henman to discuss his game.

"I needed to start being more aggressive at the right times in rallies," he said.

"Tim understands so much about the game that he can give advice on anything. Tonight, I made the right decisions."

In other matches, Sweden's Joachim Johansson made a disappointing return to action having been out since July with a shoulder injury.

The former US Open semi-finalist lost 6-3 4-6 6-3 to American Sam Warburg.