Sixth-seeded Alexander Zverev has doubled-faulted 17 times in his US Open round of 16 exit to Diego Schwartzman.
The Argentine took full advantage of his German opponent’s service issues to close out a 3-6 6-2 6-4 6-3 victory on Arthur Ashe Stadium in three hours and eight minutes.
Zverev’s serving problems have dogged him for months and they came back in force against Schwartzman, who advanced to the quarter-finals at Flushing Meadows for the second time in the past three years.
The diminutive 20th seed broke serve eight times with the almost two metre-tall Zverev winning just 32 per cent of second-serve points and amassing 65 unforced errors.
“Alex had many problems with his serve. I am a big returner and took my chances,” Schwartzman said.
“That helped me a lot. I knew I had the chance to win this match.”
Zverev was hit with a point penalty for swearing in the final set to put Schwartzman up 5-2.
The world No.6 pleaded in vain he had been unaware of being warned before for slamming the ball into the crowd and was backed up by Schwartzman, but the point penalty stood.
The relentless Schwartzman played solidly from the baseline to deny Zverev his first quarter-final appearance in New York and move through to a meeting with second-seeded Rafael Nadal or 22nd-seeded Croatian Marin Cilic.
For Schwartzman the win was just his sixth in 28 attempts against a top-10 opponent, sending him through to the last eight at a major tournament for only the third time.
“It was great to play with this crowd, they helped in every important moment,” Schwartzman said.
Earlier on Monday, Matteo Berrettini, the 24th seed, roared through to the last eight of a grand slam for the first time with a clinical 6-1 6-4 7-6 (8-6) win over Andrey Rublev.
The unseeded Russian had beaten Stefanos Tsitsipas and Nick Kyrgios in earlier rounds but Berrettini’s 37 winners proved too much in the two hour and 11 minute encounter.
“My weapons were really good today. I was mixing up my tennis,” Berrettini said.
He carved out 10 break point chances and converted four of them on his way to victory to become the first Italian to reach the last eight at the US Open since Corrado Barazzutti 42 years ago.
Next up for Berrettini is the winner of the clash between 13th-seeded Gael Monfils and unseeded Spaniard Pablo Andujar.