In a battle between two of the best movers on the men's circuit, ninth-seeded de Minaur fought off seventh-seeded American Frances Tiafoe 6-2 4-6 6-4 in Toronto on Sunday (local time) as he advance to join countryman and defending champion Alexei Popyrin in the quarters.
De Minaur got off to a sizzling start, racing through the first set 6-2 before Tiafoe regrouped in the second to force the match into a decider.
The Australian's renowned return game held him in good stead as he converted five of the 10 break points he generated during the match, compared with the American's three of seven chances.
However, de Minaur will be looking for an improvement on his service game for his quarter-final, after landing just 42 per cent of his first deliveries.
He is set to face young American fourth seed Ben Shelton who rallied to outlast 13th-seeded Flavio Cobolli of Italy 6-4 4-6 7-6 (7-1), overcoming a 4-2 deficit in the final set.
Tiafoe hit more aces than de Minaur (10 to six) and more winners (29 to 23), but the American also gave up more free points with unforced 49 errors, compared with 35 from his opponent.
"It was never going to be easy, and Frances has the ability to turn the switch on whenever he wants, so it is always very tricky to put him away,'' de Minaur said after the match.
"I think I battled him, myself and the conditions, and I am happy to sneak away with the win today.''
De Minaur has found a rich vein of form in the countdown to the year's final major, the US Open on the hard courts at Flushing Meadows in New York, which starts on August 24.
The Australian is already a two-time US Open quarter-finalist (2020 and 2024) and has his sights set on making his first grand slam semi-final, having reached the quarters of all four majors.
His timing could not be better, de Minaur coming to Toronto after clinching the Washington Open singles championship last week, his 10th ATP Tour title.
The Washington event was also played on hard courts, making the Aussie one of the most in-form players on the surface.
His win over Tiafoe stretched de Minaur's winning streak to eight matches.
De Minaur has previously reached the Canadian Open final, losing the 2023 decider against Italy's Jannik Sinner, who has since risen to the top of the world rankings.
Having advanced from the round of 16 a day earlier, 18th seed Popyrin will take on top-seeded German Alexander Zverev in their quarter-final on Monday (Tuesday AEST), with de Minaur in action again a day later.
Earlier, sixth-seeded Audrey Rublev led Alejandro Davidovich Fokina of Spain 6-7 (7-3) 7-6 (7-2) 3-0 when Davidovich Fokina retired because of exhaustion.
Rublev will face the winner of the late match between second-seeded Taylor Fritz and Jiri Lehecka.
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