Pouille, 22 and ranked 25th in the world, lived up to the promise of his quarter-final run at Wimbledon, emerging from a roller-coaster ride with a 6-1, 2-6, 6-4, 3-6, 7-6 (8/6) triumph over the Spanish superstar yesterday.
The defeat leaves Nadal -- forced out of the French Open third round with a wrist injury that also saw him miss Wimbledon -- without at least one Grand Slam quarter-final appearance for the first time since he was a teenaged tour newcomer in 2004.
Fifty-two winners from Nadal -- whose attacking response saw him come out a winner on 35 of 48 forays to the net -- weren't enough.
The taut battle came down to the fifth-set tiebreaker and Nadal, trailing 3-6, showed his mettle by saving three match points -- the third on Pouille's serve.
Then he smacked a forehand into the net to give Pouille one more chance and the French player pounced on it with a blazing forehand that kissed the sideline.
"It was a very close match, anything could have happened," said Nadal, who opened the fifth set with a break but couldn't hold onto it, dropping his own serve in the eighth to make it 4-4 and set the stage for the tiebreaker.
The four-hour, seven-minute contest entranced the crowd in Arthur Ashe stadium, where Pouille recalled admiring Nadal as a youngster.
"When I was younger I used to watch all his matches on (Ashe) and now it's me," said Pouille, who has won three successive five-setters to reach the last eight.
He next tackles 10th-seeded compatriot Gael Monfils, a 6-3, 6-2, 6-3 winner over Cypriot Marcos Baghdatis.
Ninth-seeded Jo-Wilfried Tsonga also advanced, downing Jack Sock, the last American man left in the draw, 6-3, 6-3, 6-7 (7/9), 6-2.
Against Tsonga he mustered only five aces and was broken six times by the 2008 Australian Open runner-up, who has reached at least the semi-finals of every Grand Slam except this one.
Tsonga next faces either world number one and defending champion Novak Djokovic or Kyle Edmund, a 21-year-old Briton who is in the last 16 of a Grand Slam for the first time in his first appearance in the US Open draw.
Djokovic, 9-0 in US Open fourth-round appearances, struggled through a first-round victory over Jerzy Janowicz but hasn't broken a sweat since.
The extra rest may prove providential for Djokovic, who has battled a left wrist injury and received treatment on his right arm during his win over Janowicz.
The remaining round of 16 matches were scheduled for Monday, when world number two Andy Murray will take on Bulgarian Grigor Dimitrov.
Third-seeded Stan Wawrinka, sixth-seeded Kei Nishikori of Japan, eighth-seeded Austrian Dominic Thiem and former champion Juan Martin del Potro will also battle for quarter-final berths.
