For the third consecutive match, the Spaniard got off to a sluggish start on the hard courts in Toronto, falling behind early and double-faulting to hand Paul the first set.

Alcaraz upped his game in the second, hitting a sensational tweener for a winner to level at 3-3 and breaking at love for a 4-3 lead the next game en route to leveling the contest.

But Paul took control in the decider, smoking a backhand at the charging Alcaraz that he could not put back in play for a break and pouncing on a poorly executed drop shot from Alcaraz on match point to dismiss the top seed.

Paul will rise to a career-high ranking of at least 12 on Monday and will face Jannik Sinner in the semis.

Earlier, Alex de Minaur pulled off a gritty 7-6(7) 7-5 upset of second seed Daniil Medvedev at the Canadian Open on Friday to reach his first semi-final at a Masters 1000 event where he will face Spaniard Alejandro Davidovich Fokina.

The speedy Australian fell 5-2 behind in the opener and had to fend off three set points in the tiebreak before clinching the first set against the 2021 champion in Toronto.

De Minaur had to rally from a break down twice in the second set before showing his resilience again thanks to his brilliant return game, sealing victory on the Russian's seventh double fault.

"I'm probably most proud of my mental state," De Minaur told reporters.

"Throughout the whole match, I thought I was very level-headed and at no point in that match did I feel frazzled at all," he said.

"I knew my game plan. I stuck to it. I stayed positive. And I knew that any small chances I was going to get, I was going to have to take them and try to be aggressive and, you know, it worked out. So extremely happy with that."

Up next is a meeting with red-hot Spaniard Alejandro Davidovich Fokina, who swept aside American Mackenzie McDonald 6-4 6-2 earlier on Friday.

Davidovich Fokina holds a 2-1 lead over De Minaur in their head-to-head meetings.