-- NEW YORK -- There is a surprising degree of luck in tennis.
The nicked net cord, the dangerous floater avoided (or not) in the draw, a series of untimely weather delays -- they can ultimately mean the difference between winning and losing.
To that list we can now add the combination of an unlikely profusion of injured opponents -- and a massive upset on the other side of the draw.
During the third set of his quarterfinal against Kei Nishikori, Murray was upset that Cicak stopped play when a loud boom came from the speakers in Arthur Ashe Stadium. He complained that Cicak was being inconsistent, after earlier declining to do the same on several occasions when the crowd got loud on a point in the first set.
It was at this point that Murray, seen by some as a favorite at the US Open, began to unravel, losing seven consecutive games.
He never really recovered and No. 6 seed Nishikori went on to a rousing 1-6, 6-4, 4-6, 6-1 7-5 victory. The instant classic ran 3 hours, 58 minutes at Arthur Ashe Stadium. What does it mean?
"I'd say Novak would be the favorite," Murray said afterward.
Djokovic, who plays in Friday's other semifinal against No. 10 seed Gael Monfils, has played nine sets and six games. Yes, nine.
Wawrinka and del Potro, even if their match only goes the three-set minimum, will be at 18 sets and 13-plus, respectively.
Djokovic has had the enormous good fortune to see no fewer than three of five opponents stand down because of injuries. Jiri Vesely granted him a walkover in the second round, Mikhail Youzhny retired after six games in the third and Jo-Wilfried Tsonga decided to stop their quarterfinal match after two sets Tuesday night.
Djokovic, who has already won two of the three majors this season, needs no other assistance. He came into the US Open with an ailing wrist, which he suffered during a first-round loss at the Rio Olympics. The injury kept him out of Cincinnati, and there were questions whether he'd be fully fit for New York.
During his opening-round match against Jerzy Janowicz, there were signs of trouble. Only five games into the match, Djokovic asked for a trainer, who massaged his right arm. Djokovic ultimately prevailed, but afterward, he would not elaborate on the extent of the injury, merely saying it wasn't the right time to talk about it.
Since then, Djokovic hasn't been pushed. He has played six completed sets and hasn't lost more than four games in any. Now, the biggest threat to his title is gone. Granted, Djokovic has dominated their head-to-heads, leading 24-10, but Murray came into the US Open prevailing in 26 of his past 27 matches.
"This Slam, in particular, I think for all of the players, especially the ones, you know, that have done well over the summer period on the hard courts, it's, you know, a tough one," Murray said.
Nishikori played cleverly, mixing up his serve, moved forward when he could and hit a large number of drop shots. He won 27 of 39 points at net, nearly more than twice as many as Murray.
After winning the bronze medal in singles in Rio, Nishikori has some momentum going -- and a comfortable feeling in his second US Open semifinal in three years.
"Two years after, I have a great memory here," Nishikori said. "I think this is a great opportunity to come in a semifinal again."
But unlike Djokovic, he might be tapped out.