Kyrgios stuns Medvedev at US Open, Gauff advances

Australia's Nick Kyrgios sent defending champion Daniil Medvedev tumbling out of the US Open on Sunday as US teenager Coco Gauff reached the quarter-finals for the first time.

The notoriously temperamental 23rd-seeded Kyrgios produced some scintillating shot-making on his way to a superb 7-6 (13/11), 3-6, 6-3, 6-2 win over the world number one from Russia.

Kyrgios, who was beaten by Novak Djokovic in the Wimbledon final in July, showed grit and composure to save three set points in the opening set before holding his nerve to win an epic tie-break 13/11 before a raucous Arthur Ashe Stadium crowd.

Although Kyrgios dropped the second set, he roared back to dominate Medvedev in the third and fourth sets to clinch victory in 2hr 53min.

"It was an amazing match, obviously Daniil as the defending champion had a lot of pressure on his shoulders, but I've been playing amazing the last couple of months," Kyrgios said after the win.

"What a place to do it -- packed house in New York. I'm extremely blessed."

Medvedev meanwhile said the mercurial Kyrgios had elevated his play to the same level as great such as Rafael Nadal and Djokovic.

"Nick today played kind of at the level of Novak and Rafa," said the 26-year-old after seeing 21 aces and 53 winners whizz past him.

"If he plays like this until the end of the tournament, he has all the chances to win it."

Kyrgios will face Karen Khachanov in the quarter-finals on Tuesday. Khachanov equalled his best performance in a Grand Slam event by defeating Spanish 12th seed Pablo Carreno Busta in a 3hr 21min five-set thriller.

The 27th-seeded Khachanov dug deep to down Carreno Busta 4-6, 6-3, 6-1, 4-6, 6-3 on the Louis Armstrong Stadium.

Elsewhere in the fourth round on Sunday, fifth seed Casper Ruud