Andy Murray stumbled at the end of the first set, dropping four points in a row. He faltered for a fleeting moment at the end of the second set, too, missing a simple volley after his opponent's between-the-legs shot.
What truly mattered most in Murray's fourth-round match at the U.S. Open, of course, was the ultimate result, and the defending champion wound up beating 65th-ranked Denis Istomin of Uzbekistan 6-7 (5), 6-1, 6-4, 6-4 on a windy Tuesday night.
The third-seeded Murray reached the quarterfinals at Flushing Meadows for the third consecutive year.
He was 0-4 in Grand Slam finals until his title at last year's U.S. Open. He added a second major championship this July by becoming the first British man since 1936 to win Wimbledon.
Now Murray will play No. 9 Stanislas Wawrinka of Switzerland, who reached his second U.S. Open quarterfinal by eliminating No. 5 Tomas Berdych of the Czech Republic 3-6, 6-1, 7-6 (6), 6-2.
Istomin was making his debut in the fourth round at a major tournament Tuesday, and trying to become the first player from his country to reach a Grand Slam quarterfinal. His power-based game occasionally gave Murray fits under the lights in Arthur Ashe Stadium.
Notably, Murray came apart after leading 5-3 in the opening-set tiebreaker.
First, Istomin hit a forehand winner to close a 27-shot exchange. Then Murray, distracted before his service toss by a shout from the stands, double-faulted. A forehand into the net by Murray gave Istomin a set point. And Murray ended the set by pushing a backhand wide on a 12-stroke point.
Istomin shook his racket and screamed, while the folks sitting in his guest box rose to their feet, yelling right back at him.
Most of the second set was no cause for celebration, however. Istomin, wearing yellow-framed eyeglasses, got broken right away and trailed 3-0 after 12 minutes.
A highlight-worthy point came when Murray tried to even the match at a set apiece while serving at 5-1 in the second. With both men near the net, Murray stretched to hit a lob volley that sent Istomin racing back to the baseline. His back to the court, Istomin smacked a no-look shot through his legs. The ball made it across the net, but weakly, and Murray should have been able to respond with an easy, tap-in volley. Instead, he flubbed it, dumping the ball in the net to make the game score 15-30, and immediately put his hand to his face.
Not to worry, though. Murray won the next three points to take that set.
There was more shakiness from Murray in the third set, in which he went up a break, only to lose serve to make it 3-all.
But he broke right back for a 4-3 edge, and was back on his way to a victory that improved his record over his last five Grand Slam tournaments to 30-2.
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