Murray played both his opening matches in Cincinnati in the afternoon heat
Andy Murray fought back from a set down to clinch a 4-6 6-3 7-6 (7-4) victory over Ernests Gulbis in the third round of the Cincinnati Masters.
Gulbis broke twice to power into a 4-1 lead, before Murray broke back, but the Latvian held on to take the first set.
An improved Murray hit back to take the second set before then winning a hard-fought third on a tie-break.
The Scot, who next faces American wildcard Mardy Fish in round four, now has a seven-match winning streak.
The 23-year-old British number one said the heat in Cincinnati, which reached over 32C, made playing conditions difficult.
"It was very warm and I was struggling to get control," said Murray, who won the Toronto Masters last week.
"Gulbis was hitting huge. He was comfortable when he was dictating points. I then began to make some first serves and then made sure he would have to play some great tennis to win the tie-break."
Murray now faces Fish in the last eight. The pair have met six times and share the wins, but the American world number 36 came out on top in their last two encounters.
"When I played against him both times this year, I was struggling with my form," added Murray.
"But I've previously had some good results against him and I'm playing a lot better than I was a few months ago.
"I need to up my game and hopefully I can get given an evening match."
What's the difference between winning by two points in a tie-breaker and losing by two points? A little bit of good play and luck also
Murray, who was clearly suffering in the heat, battled back after losing the first set to win the second and level the match.
Both players struggled in the second set with Murray chastising himself on several occasions, while Gulbis had changed racquet after smashing his first in frustration.
It was hard to separate the players going into the final set tie-break, but when Gulbis, at 3-1 down, tried a straightforward smash he was dazzled by the sun and failed with his attempt.
Murray eased to 6-1 but wasted his first three match points before taking the third.
World number one
Rafael Nadal saved a match point against Frenchman Julien Benneteau to reach the quarter-finals.
The Spaniard was on the verge of exiting the tournament during the second set tie-break but fired down back-to-back aces and went on to seal a 5-7 7-6 (8-6) 6-2 win.
"Two first serve, two winners with his forehand, and I did not have an opportunity in the point, in the rally, to put him under pressure," said Benneteau. "I have no regrets on these points."
Nadal said: "A match like this gives me a lot of confidence. A match point? Yeah, I am doing this well. I am playing aggressive. But I need to do better the next few days."
Nadal faces Cypriot
Marcos Baghdatis who beat Czech seventh seed Tomas Berdych 7-5 6-4.
Roger Federer reached the last eight without having to face Philipp Kohlschreiber.
The German withdrew because of a sore right shoulder which troubled him during practice on Thursday.
Federer had only played 28 minutes of his opening match against Denis Istomin when the Uzbek qualifier injured his right foot.
The Swiss will face Russian sixth seed
Nikolay Davydenko, who had an impressive 4-6 6-3 7-5 win over Spain's David Ferrer.
Meanwhile, world number three
Novak Djokovic beat Argentine David Nalbandian 6-1 7-6 (9-7) to advance.
The Serbian now faces American
Andy Roddick, who came through a tense night match 6-4 6-7 (7-9) 7-6 (7-5) against Swedish fifth seed Robin Soderling.
"What's the difference between winning by two points in a tie-breaker and losing by two points?" said Roddick. "A little bit of good play and luck also."