NEW YORK -- Canadian Felix Auger-Aliassime has been knocked out of the U.S. Open, suffering a loss in straight sets to No. 2 seed Dominic Thiem on Monday.

The 20 year old from Montreal battled the Austrian to a tiebreak in the first set before struggling at the net and committing 51 unforced errors in the 7-6(4), 6-1, 6-1 loss.

Auger-Aliassime came into the tournament as the No. 15 seed and is the first player born in the 2000s to make a Grand Slam fourth round.

He wasn't the only Canadian to be ousted from the tournament on Monday, however.

Vancouver's Vasek Pospisil was beaten in straight sets by No. 21 seed Alex de Minaur of Australia.

Pospisil, ranked 94th, said he was battling quadricep and abdominal strains when he failed to convert on four set points in the first set en route to a 7-6 (6), 6-3, 6-2 loss.

"I just tried to manage it but it impacted my serve the most out of all my strokes, so that was not ideal," he told reporters after the match. "But it is what it is ... It's a Grand Slam so it's very physical and at some point your body's going to take a beating and I think it definitely affected me a little bit today."

De Minaur broke Pospisil twice in the second set and rolled to victory, sending the 21 year old to his first Grand Slam quarterfinal.

De Minaur's speed is difficult to keep up with, Pospisil said.

"What's most impressive is that he never breaths," he said with a laugh. "He runs side to side and he's never out of breath. He defies the laws of biology, I guess. It's pretty impressive but he's definitely a freak of nature."

Pospisil, 30, was one of a record three Canadian men to reach the round of 16 at the U.S. Open.

"It's a great time for tennis in Canada right now, for sure. It's cool to be part of it," Pospisil said.

No. 12 seed Denis Shapovalov of Richmond Hill, Ont., beat No. 7 seed David Goffin in four sets on Sunday night to set up a quarterfinal match against No. 20 seed Pablo Carreno Busta of Spain on Tuesday.

Carreno Busta advanced when the top-ranked Novak Djokovic was kicked out of their match for accidentally hitting a line judge in the throat with a tennis ball after dropping a game.

Shapovalov is the first Canadian man in history to reach the U.S. Open quarterfinals. Previously, Canadian men were 0-12 in the round of 16.

Pospisil upset No. 25 seed Milos Raonic of Thornhill, Ont., and No. 8 seed Roberto Bautista Agut of Spain before his surprise run came to an end against de Minaur.

De Minaur, who beat No. 11 seed Karen Khachanov of Russia on Saturday, and Pospisil both came back from 2-1 set deficits to prevail in the third round.

It has been a promising last 12 months for Pospisil, who missed the first half of last year after back surgery. He helped Canada reach the Davis Cup final late last year and has an 11-6 record this year, including a runner-up showing at a tournament in Montpellier, France.

Pospisil is projected to move up to No. 72 in the rankings next week. He reached a career high of No. 25 in 2014 when Pospisil reached his first and only Grand Slam quarterfinal at Wimbledon.

Meanwhile, Ottawa's Gabriela Dabrowski and American partner Alison Riske lost 6-4, 6-2 to Americans Asia Muhammad and Taylor Townsend in a women's doubles quarterfinal on Monday.

Shapovalov and partner Rohan Bopanna of India were scheduled to play a men's doubles quarterfinal against Jean-Julien Rojer of the Netherlands and Horia Tecau of Romania later Monday.

This report by The Canadian Press was first published Sept. 7, 2020.