Stanislas Wawrinka followed up his win over Andy Murray by prevailing in a five-set epic against Sam Querrey to reach the last eight of a grand slam for the first time at the US Open.
The Swiss 25th seed triumphed 7-6 (11-9) 6-7 (5-7) 7-5 4-6 6-4 in a match lasting just shy of four and a half hours to seal a quarter-final tie with Mikhail Youzhny, who saw off the challenge of Tommy Robredo earlier in the day.
The first set went with serve to set up a lengthy tie-break, which Wawrinka eventually took 13-11.
But he then wasted four set points while serving at 5-4 in the second set to allow Querrey to force a tie-break, and the sole remaining home hope took full advantage of his second chance.
Having hit back from an early break in the third set, Wawrinka then broke in the 11th game to re-establish his lead, but 20th seed Querrey continued to battle and sent the game to a decider as he managed to take the fourth set on his sixth set point.
However, Wawrinka, who continued to receive treatment to the thigh he injured against Murray, finally sealed the win as he claimed the crucial break in the 10th game to take the final set.
He said: "It's the first time for me, so for sure I am very happy with that. It's something very important, and I knew before the match it was going to be tough, but I was really focused on the match, on staying with him."
Twelfth seed Youzhny had earlier secured a 7-5 6-2 4-6 6-4 win over Spain's Robredo.
The Russian, a semi-finalist at Flushing Meadows in 2006, was slow out of the blocks but Robredo failed to capitalise.
A single break opportunity in the 11th game saw Youzhny take the lead. He took the set to 2-0 with a more measured second se tthat left Robredo banging his racquet off the ground.
Robredo recovered his composure to take the third set but his hopes were quickly ended as Youzhny broke in the fifth game of the fourth set and held on for the win.
Speaking after his victory, Youzhny said: "I actually liked how I played today.
"Of course, I made some mistakes. I was a little bit lucky in the fourth set but I also missed some chances in the third set.
"I have now reached two quarter-finals in the year (after the French Open) and maybe it will mean I will start to play a little bit more consistently, not just really well in some matches and not in others."
Fernando Verdasco triumphed after falling two sets behind in an all-Spanish match-up in Louis Armstrong Stadium.
David Ferrer, seeded 10th, was the unlucky loser as he went down 7-5 7-6 (10/8) 3-6 3-6 6-7 (4/7).
Eighth seed Verdasco looked down and out after two hard-fought defeats in as many sets but grew as the game went on and played some thrilling shots in a decisive fifth-set tie-break.
He will now play the winner of the final last-16 game between two more Spaniards - number one seed Rafael Nadal and 23rd seed Feliciano Lopez.