Schwartzman improved to against Fritz and avenged an earlier season defeat to the American in Monte Carlo. The fifth-seeded Fritz held an early break advantage in the first set, but Schwartzman dug back in by extending rallies and going for heavy forehand finishes. He saved three set points to force a tiebreaker, where the two suddenly struggled to find their range and rhythm. Serving atSchwartzman committed three successive unforced errors, but was bailed out by Fritz, who hit his third double fault before netting a backhand to drop the set.
Click here for Live Guide. Schwartzman, the 20th seed, won and will next face Rafael Nadal who overcame Marin Cilic in four sets. A frustrated Zverev was docked a point for an obscenity in the final set after earlier hitting a ball into the crowd.
French 13th seed Gael Monfils cruised past unseeded Spaniard Pablo Andujar to make the last eight.
Monfils, 33, broke serve six times and did not face a break point as he won in one hour and 26 minutes to set up a meeting with Matteo Berrettini. Italian Berrettini, seeded 24th, saw off Russian Andrey Rublev to reach a Grand Slam quarter-final for the first time.
Berrettini, 23, had failed to progress beyond the first round in two previous attempts in New York. He served for the match at in the third set and, though unseeded Rublev was able to break him for the first time, the Italian secured victory in the resulting tie-break.
Defending champion Osaka out of US Open Frustrated Zverev falls short again After three lengthy sets featuring 10 breaks of serve, Schwartzman, 27, stormed into a lead in the fourth against an out-of-sorts Zverev, who served 17 double faults and made 65 unforced errors.
Zverev clawed a break back but, following a previous code violation for hitting the ball into the crowd, he was then docked a point for an audible obscenity on game point, which gave Schwartzman a lead. The year-old remonstrated with umpire James Keothavong, saying he had not heard the earlier violation because of the noise of the rain falling on the Arthur Ashe Stadium roof.
Zverev found some composure to win his next service game but Schwartzman was able to convert the second of two match points with a forehand winner. The defeat means Zverev, the winner of last year's ATP Finals and seen by many as the leader of the next generation in the men's game, has still only made two Grand Slam quarter-finals - at the French Open in and I think I played great tennis," said Schwartzman.
The Argentine, who has lost all seven previous meetings with Nadal, added: "Rafa is my friend. It's always great to play against him in a quarter-final of a Grand Slam.
At 5ft 7in people thought it would be too difficult for him but he has proven everyone wrong. It's another Grand Slam where Zverev will leave with much disappointment and there will be a lot of soul-searching with him and his team after that loss.