NEW YORK • First came the rain, then some electronic thunder and, in time, a lightning strike of Andy Murray's racket across the net.
On a day that began and ended under bright, sunny skies, a US Open men's quarter-final seemed to pivot on a brief rain shower, and it was Murray who suffered.
The No. 2 seed - and the choice of some to win the tournament - had been cruising at the Arthur Ashe Stadium on Wednesday.
But midway through the second set, a light rain began to fall.
The retractable roof, which is emerging as one of the main characters of this Open, was closed, and everything changed.
Kei Nishikori, this year's sixth seed and the runner-up in 2014, came back and stunned the Scot 1-6, 6-4, 4-6, 6-1, 7-5, in a thrilling duel that was determined, at least one man thought, by the roof.
"I think definitely under the roof he was able to dictate more of the points," Murray said.
Nishikori reached the semi-finals at a Major tournament for only the second time and will face No. 3 Stan Wawrinka, who defeated Juan Martin del Potro 7-6 (7-5), 4-6, 6-3, 6-2.
The Japanese, who had lost seven of his last eight matches to Murray, has not always played to his potential. But the US Open is becoming his favourite Grand Slam event.
"I love the crowd," he said. "It makes me more motivated. It's little bit different than other Grand Slams. It's louder, and it's more like a big party on the court."
Murray enjoyed that feeling when he took the title in 2012 but, even after an outstanding summer in which he won the Wimbledon title and the gold medal at the Rio de Janeiro Olympics, he may wonder about this match.
Was it really the closing of the roof that changed the conditions, or was it his preoccupation with it?
Many players believe that when the roof is closed, it creates slower conditions because of increased humidity and an absence of wind.
As a rule, that would help those looking to return big serves because it slows those serves down.
Murray has a better serve than Nishikori, so he thought that was a critical difference in the match; his serve was broken nine times, including thrice in the final set.
"I started off serving pretty well," said Murray, who broke back eight times. "It obviously slows the conditions down, so it becomes easier; he started returning a bit better."
Perhaps as important, Nishikori talked about "a lot of things" to his coach Michael Chang while the roof was being closed, and they made some tactical adjustments.
He said: "Yeah, I tried to change something. It worked well. For sure it helped today's game."
He grew more confident and Murray more agitated, with his distress culminating in an overhead smash of his racket on the net in the penultimate game of an unusual match.
It featured a loud electronic noise, which came from a malfunctioning courtside sound processor, interrupting play as well as a butterfly that loitered about the net during the fourth set.
Murray was distracted by these incidents while Nishikori kept his cool to win the match.
Later, del Potro broke down in tears as his run approached an end and he was given an ovation.
Many dressed in the blue-and-white shirts of Argentina's football team sang "Delpo, Delpo" as the injury-plagued 2009 champion faced what turned out to be the last game of a match.
"I can lose the match but I will never forget this," said the former world No. 4 who came into the tournament ranked No. 142 after undergoing a series of wrist surgeries which pushed him to the verge of retirement. "It's bigger than winning any match."
NEW YORK TIMES, AGENCE FRANCE-PRESSE