Andy Murray made a special request to play Brazil’s Thomaz Bellucci later so he could rest his weary legs and the British number one conserved energy on court too with a comfortable straight-sets victory.
Murray survived two draining opening encounters against Nick Kyrgios and Adrian Mannarino in Flushing Meadows but his 6-3 6-2 7-5 win over Bellucci to reach the last 16 was far more comfortable.
Sealing progress in a brisk two hours and 11 minutes, Murray can rest up ahead of the second week, which starts against South Africa’s Kevin Anderson and could follow with Stan Wawrinka, Roger Federer and Novak Djokovic.
The surprise of the day saw American Donald Young fight back from two sets down to beat Serbia's 22nd seed Viktor Troicki 4-6 0-6 7-6 (7/3) 6-2 6-4.
It is the second time this tournament the 26-year-old had battled back from the brink and he will now play fifth seed Stan Wawrinka for a place in the last eight.
Murray’s was the last match on, playing under the lights of Arthur Ashe Stadium, and the Scot was thankful for the extra hours to recover from both fatigue and a niggling bout of cold.
“I just asked if I could play slightly later rather than first or second,” Murray said.
“Today I felt much better. I slept during the day yesterday two or three times.
“Today I got up, and I slept again before coming out to the courts. I felt much, much better. My voice feels like normal again.
“It’s still dull obviously, but it feels more normal today and not blocked up or anything any more, which is good.”
Murray showed few signs of weakness, breaking Bellucci’s serve five times during the match and dropping his own just once, early in the first set.
The Scot was typically tenacious in his defence and too quick in attack as Bellucci struggled to cope with his opponent’s touch and creativity.
“I felt like I played well,” Murray said.
“In these conditions, it’s a bit easier to control the ball. The ball was not bouncing as high. It was a bit flatter.
“In the conditions the other day, when you tried to flatten the ball out, it was quite easy for it to sail on you.
“It was harder to serve today. It was much slower conditions to serve in so there were less aces but then obviously returning’s a little bit easier, as well.
“So I felt like I played well. But the conditions helped that, too.”
Murray boasts a strong record against Anderson having won five of their previous six encounters, including a straight-sets win in the final at Queen’s in June.
The big-serving South African has never made it past the third round in New York but is in good form after winning the Winston-Salem Open last week and beating highly-rated Austrian Dominic Thiem in round three.
“I played some good matches against him in the past,” Murray said.
“I only lost to him once in Montreal. It was a very quick, easy match.
“I lost to him there but apart from that, I’ve normally played quite well against him.
“He’s obviously playing some good stuff. He won the tournament last week. He’s had a couple of good wins here.
“Thiem is going to be one of the top players in the future – that was a pretty good win tonight. It will be a tough one, for sure.”