British number one Cameron Norrie (27) chipped away at Holger Rune's (19) defences to win 7-5 6-4 6-1 on Saturday and reach the fourth round at the US Open for the first time.
The Wimbledon semi-finalist Norrie had already beaten Rune twice this year and showed he had not lost the winning formula in sizzling conditions, making 22 unforced errors to his Danish opponent's 43.
Rune saved 11 of the 18 break points he faced in the match but was left without answers in the third set when Norrie, who had hold of the momentum, stormed through without dropping a single first-serve point.
Norrie, who had a strong run-up to Flushing Meadows after reaching the Cincinnati semi-final, next faces either Canadian Denis Shapovalov or Russian Andrey Rublev.