NEW YORK -- Novak Djokovic fended off a fading Andy Murray 7-6 (1), 6-7 (1), 6-2, 6-4 in a matchup of past US Open champions Thursday to reach the tournament's semifinals for the eighth consecutive year.
It took a while for the No. 1-ranked and No. 1-seeded Djokovic to push himself out front in a well-played, back-and-forth, 3-hour, 32-minute match that ended after 1 a.m. ET.
Djokovic broke the eighth-seeded Murray to go up 3-1 in the third set, then turned back a pair of break points in the next game.
On the first, Murray sailed a backhand long to end a 28-stroke point, then leaned over and put a hand on his knee. On the second, he dumped a forehand into the net, then slammed his racket against his right thigh and yelled.
Soon, Murray was turning to his box to say, "Nothing in the legs."
In the fourth set, a trainer came out to deliver a heat pack to Murray.
Murray had back surgery a year ago, and in his first-round match in New York last week, he barely managed to overcome cramps all over his body. Murray had looked fine since then, but he couldn't sustain his top form throughout the physically demanding quarterfinal against Djokovic, who won the US Open in 2011 and has played in the past four finals.
Djokovic will face Kei Nishikori in Saturday's semifinals.
Nishikori earlier became the first man from Japan to reach the US Open semifinals in 96 years, outlasting third-seeded Stan Wawrinka of Switzerland 3-6, 7-5, 7-6 (7), 6-7 (5), 6-4.
Their match went 4 hours, 15 minutes, and the 10th-seeded Nishikori managed to shake off any lingering exhaustion from his previous victory, which lasted 4:19 and ended at 2:26 a.m. Tuesday, equaling the latest finish in tournament history.
Nishikori began slowly against the Australian Open champion, but eventually got his bearings and used crisp returns and strong net play to edge ahead.
"Actually, I started a little bit tight, but my body was OK," Nishikori said in an on-court interview. "I don't know how I finished ... but I'm very happy."
The last Japanese semifinalist at the US Open was Ichiya Kumagae in 1918. No man from the country had made it to the final four at any major tournament since Jiri Satoh at Wimbledon in 1933.
Nishikori, 24, already was the first Japanese man to be ranked in the ATP's top 10, having climbed to No. 9 in May. He came into the US Open without a lot of proper preparation, because he was sidelined after having a cyst removed from his right foot in early August.
Nishikori, who is coached by 1989 French Open champion Michael Chang, had never eliminated top-10 opponents in consecutive matches at a major tournament. The fourth-round marathon win against No. 5 Milos Raonic put Nishikori in his second career Grand Slam quarterfinal; he lost in that round at the 2012 Australian Open.
Wawrinka had won 15 of his last 16 hard-court Grand Slam matches, a stretch that includes a run to his first major semifinal at last year's US Open and his first Grand Slam championship at the Australian Open.
Information from The Associated Press was used in this report.