Andy Murray vs. Denis Istomin: Score and Recap from 2013 US Open

Defending U.S. Open champion Andy Murray survived a determined upset bid from world No. 65 Denis Istomin on Tuesday, advancing to the quarterfinals with a gritty 6-7(5), 6-1, 6-4, 6-4 victory.

It appeared as though Istomin, who put forth a terrific effort, let a major opportunity slip through his grasp in the first set. 

Up a break and serving for the first set, the Uzbekistani missed on some pretty basic forehands before double-faulting to give Murray the break.

In the tiebreak, however, Murray—on track to serve for the set—returned the favor with a double fault of his own to help keep Istomin alive. With that new-found chance, the challenger would go on to win this dramatic point, courtesy of the U.S. Open's Twitter account, and eventually the set:

The 53-minute opening set was just about as close as you could imagine: Twelve winners from Murray, 11 from Istomin. Fourteen unforced errors from Murray, 10 from Istomin. Thirty-seven total points from Murray, 41 from Istomin. 

Unfortunately for Istomin, however, it apparently served as a wake-up call for Murray. 

The World No. 3 got an early break in the second set, showing a noticeable increase in energy level and aggression. He then subsequently put his foot on the gas pedal, earned another break shortly after and cruised to a 6-1 second-set victory in just 32 minutes. 

This was really the only thing that went wrong for the Brit in the entire set:

Istomin got a break in the third set but showed far too much inconsistency and made a few head-scratching moves as Murray broke him twice and took control of the match. 

In the fourth set, Istomin continued to admirably fight and hold serve, but Murray eventually got a late break to finally close out the more than three-hour match:

Murray certainly wasn't perfect on the night. He hit 35 unforced errors, served up five double faults, didn't come out with a sense of urgency and noticeably let his frustration get the best of him on a few different occasions. It was a sloppy performance. 

But he was crucially accurate with his forehand when he had to be, and he controlled the net, winning 32 of 38 points when he moved forward. 

Although it wasn't always pretty, Murray held off an admirable, never-give-up effort from Istomin—who deserves plenty of credit himself—and made smart, tactical adjustments as the night went on, eventually showing flashes of the player who was crowned champion in New York last year.

He gets a stiff challenge in the quarterfinals against Stanislas Wawrinka, who just beat No. 5 Tomas Berdych in four sets and has always had loads of potential.