World No 1 and defending US Open champion Rafael Nadal was forced to stave off Russia's Karen Khachanov in four spellbinding sets to reach the last 16 on Friday.
Nadal was forced to battle back from a set down under the closed roof of Arthur Ashe Stadium to come through 5-7 7-5 7-6 (9-7) 7-6 (7-3) in a brutal encounter lasting four hours and 23 minutes.
The Spaniard will now take on Georgia's world No 37 Nikoloz Basilashvili who reached the fourth round of a Grand Slam for the first time by seeing off Argentina's Guido Pella 6-3 6-4 1-6 7-6 (7-4).
Nadal said: "It has been a tough situation, a great opponent. I'm very happy to be through. Probably there's things to work on for the next match but the victory means I have the chance to do it."
Up-and-coming Khachanov had failed to take a set off the imperious Nadal in any of their four previous meetings, but finally served out a nervy opener on his fourth set point opportunity.
A rain delay at 5-5 in the second set meant a short delay so that the roof could be closed. That seemed to help Nadal, who despite having his right knee strapped during the break in play, took his only opportunity to bounce back.
The third set went with serve and had to be settled by a tie-break. That proved to be a crucial turning point in the match as Khachanov saved four set points, but it was Nadal who showed unbelievable composure to seal it following a gruelling 39-shot rally.
That appeared to knock the stuffing out of the 22-year-old world No 26, who was broken early in the fourth. But Nadal tightened when serving for the match in the 10th game allowing Khachanov to find a second wind to hit back.
Nadal was forced to save a set point in the next game as this classic headed into another tie-break.
The 17-time Grand Slam champion found his touch to march away with it after an incredible encounter as he reached the fourth round in New York for the 10th time.
Austrian ninth seed Dominic Thiem reached the last 16 for the fourth time in five years in a match lasting three hours and 19 minutes.
Thiem defeated America's Taylor Fritz 3-6 6-3 7-6 (7-5) 6-4 and will tackle 2017 runner-up Kevin Anderson for a place in the quarter-finals.
"I've always lost in the fourth round so I think it's time I get to the quarters," said Thiem.
Anderson outlasted Canadian teenager Denis Shapovalov 4-6 6-3 6-4 4-6 6-4 in a match that saw the new Louis Armstrong Stadium roof closed for the first time at the tournament.
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Tennis is back on Sky Sports screens with the Laver Cup in September while we will also have coverage of the ATP Finals in November with every match live on Sky Sports. But first, we will be across the final major of the year in New York as the US Open right through to the final with live blogs, reports, features and reaction.