"Finishing matches at 3 in the morning is not good".
Murray hit a forehand long to fall level 3-3, then slammed his racquet to the court, recovered it and hit three winners to reach match point, winning when Copil netted a backhand.
"I don't think I should be put in a position like that", Murray said. "Not good for fans, not good for TV, nobody".
Murray, whose last prior hardcourt appearance was in March 2017 at Indian Wells, played only two June grasscourt events in his comeback prior to coming to Washington, where he played three of the week's four longest matches.
"When you're expected to come back and perform the next day, I think that's unreasonable".
The extraordinarily late finish to his match with Copil gave him little time to recover for his quarter-final and in the aftermath he voiced his annoyance at the scheduling, hinting that he may withdraw to preserve his exhausted body. Murray's withdrawal, announced earlier on Friday, gave Australia's Alex de Minaur a free pass to the semi-finals where he will meet the victor of Andrey Rublev and American Denis Kudler.
"I'm giving my view right now as someone who's just come back from a very, very long injury layoff".
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Murray said in a statement on the ATP website: "I won't be able to play my match tonight". Zverev joked after advancing, "I think I'm the only one that's allowed to buy a drink in the US, right?"
"I do understand 3 a.m.is very hard for everyone", O'Brien said. At the very least, he doesn't feel it should have to be a decision he has to make.
Zverev came from behind to beat Nishikori 3-6 6-1 6-4 to eliminate him for the second consecutive time from the tournament.
Norrie won almost three-quarters of his first serve points as he dismissed the fourth seed and world number 25 to reach his second successive ATP Tour semi-final.
Germany's third-ranked Zverev, seeking his fifth final of the season and third title of the year after Munich and Madrid, dispatched seventh-seed Nishikori, the 2015 champion, as he did in last year's Washington semi-finals. By the time you finish doing recovery and everything it's 5.30 or 6 o'clock in the morning.
He will instead play next at the Masters event in Cincinnati, which begins a week on Monday, as he continues his build up to what is expected to be his first grand slam tournament since last year's Wimbledon at the US Open later this month.
Murray's third-round victory over Marius Copil ended just past 3 a.m. on Friday, after rain delayed the start of Thursday's action for 2 1/2 hours.