The Australian continued his fine form in Montreal, needing just 64 minutes to dismantle De Minaur 6-2, 6-3 in a one-sided affair.
In fact, just 11 minutes into the opening set, Kyrgios had already established a 4-0 lead. He closed it out with hyper-aggressive tennis, winning the final two points via serve and volley.
Kyrgios' serve continued to dominate in the second set, racking up eight aces for the match as well as crushing 25 winners, overwhelming de Minaur. The victory comes 24 hours after upsetting world number one Daniil Medvedev.
"Incredibly tough after yesterday's big high, playing Daniil, and the crowd was amazing," said the 27-year-old after the match, as per atptour.com.
"It was a day I'll probably never ever forget," Kyrgios said of his upset win.
"Today was really hard mentally for me to go out here and play Alex. We're such good friends and he's been having such a good career so far and carrying the Australian flag for so long. It was just tough mentally. It's never easy to play a player like that, especially if they're Australian.
"I just got out here and got the job done. I played the way I had to play. He's a hell of a player. If you play to his strengths, he's one of the best players we have in the game and he's so fast. He's going to have a hell of a career."
After his memorable win over Medvedev, Kyrgios tugged the heartstrings of fans around the world with a message to his mother. After writing 'Be strong Ma' on the camera lens, he told the media about his mom struggling with illness in hospital.
Next up for Kyrgios is eighth seed Hubert Hurkacz who edged Albert Ramos-Vinolas 6-7(6), 6-2, 7-6(3) to reach the last eight.