Unseeded American Ben Shelton took down 14th-seeded compatriot Tommy Paul in four sets on Sunday to reach his second Grand Slam quarter-final of the year at the US Open.

The 20-year-old Shelton avenged his loss to Paul in the last eight of the Australian Open, winning 6-4, 6-3, 4-6, 6-4 to become the youngest American to reach the men's quarter-finals in New York since Andy Roddick in 2002.

"Being at home here in front of an American crowd, I felt the love all week," said Shelton. "It's hard to believe that I'm playing on Arthur Ashe right now with the stands completely full."

The world number 47 plays the winner between 10th seed Frances Tiafoe and Australian wild card Rinky Hijikata for a place in the semi-finals.

Shelton arrived at his second US Open with a tour-level record of 12-20 this season, having failed to win multiple matches at any of the 18 events he had played since Melbourne.

Nine of his 16 victories in 2023 have now come at Grand Slams. Shelton reached the second round at Wimbledon after losing his opening match at the French Open.

He belted two serves clocked at 149 mph (240 km/h) -- the fastest of the tournament -- to open up a 4-1 lead in the third set against Paul but then lost five games on the spin.

Shelton, a former college champion who only turned professional last year, drew on the experience of his breakout Australian Open run to finally get over the line after two hours and 49 minutes.

"I really learned how to be mentally tough," he said. 

"When I was playing in Australia after a long week... I realised how important it was to believe in myself, that I could go the distance emotionally and physically."

He added: "We don't panic. There's no panic over there (in his players' box)."

mw/rcw