Frustrated world number one Carlos Alcaraz was knocked out of the ATP Toronto Masters 6-3, 4-6, 6-3 on Friday as American Tommy Paul ended the Spaniard's 14-match winning streak.

Top-seeded Alcaraz was unable to escape the poor form that has plagued him all week as he prepares for a US Open title defense starting in just over two weeks.

The 20-year-old muttered to himself and chastised his play during a match lasting more than two and a quarter hours.

"I realize I didn't play well in all of these matches," Alcaraz said. "All I can do now is practice to be better.

"I have some weeks before the US Open. But now I have to be focused (from Monday) on Cincinnati. It's a Masters 1000. It's a big tournament as well.

"I take a lot of lessons from this tournament."

Paul, ranked 14th, repeated his defeat of the Spaniard a year ago in the Montreal second round and now faces a semi-final against sixth seed Jannik Sinner, who defeated French showman Gael Monfils 6-4, 4-6, 6-3.

"It's never easy to play Gael," Sinner said. "I just tried to stick to my game plan.

"I'm having my best season, I'm happy to be in the semis. I hope to raise my level tomorrow."

Paul, meanwhile, was trying to figure out how he got past Alcaraz.

"I don't know if I think I have the recipe, but I played a really good match today," Paul said after notching another Canadian win over the Spaniard.

"I went after my shots. You can't start any points on your heels against him, he'll take advantage of it so you've really got to go after your shots early in the rally.

"Luckily I was feeling really good, playing first-strike tennis."

Alcaraz struggled early for the second straight match after barely  escaping a third-round encounter with Hubert Hurkacz.

The reigning Wimbledon and US Open champion had 27 winners and 30 unforced errors while Paul's numbers were 19 and 29.

After losing serve three times in the opening set, Alcaraz recovered enough to take the second.

But the Spaniard was well off his game, floating a volley wide to trail 4-2 in the final set.

Paul took quick advantage, advancing on his second match point from an Alcaraz return wide

"I knew he would be there in the third set," Paul said, adding: "It helps to have beaten an opponent before. That attitude is important."

- Medvedev ousted -

Second-seeded Daniil Medvedev was also sent spinning out of the tournament, falling 7-6 (9/7), 7-5 to Australian Alex de Minaur.

De Minaur will make his first semi-final appearance at the Masters 1000 level against unseeded Spaniard Alejandro Davidovich Fokina, who beat Mackenzie McDonald 6-4, 6-2.

Medvedev had won his last seven matches in Toronto, including a title run in 2021.

But the 27-year-old was unable to get past the efficient game of number 18 De Minaur, who had lost four of five previous meetings with Medvedev.

"I had to play my best tennis," De Minaur, runner-up at Los Cabos last weekend, said.

"It's always a complete chess match between us, we're both adaptable and can play many styles of tennis."

De Minaur needed more than an hour per set to prevail against the world number three.

The Aussie saved three set points in the opener and claimed the victory on his own second opportunity as Medvedev double-faulted.

Davidovich Fokina advanced in 97 minutes on his third match point against Mackenzie, who beat an injury hobbled Rafael Nadal in the second round of the Australian Open in January.

The 37th-ranked Spaniard, who reached the final Monte Carlo last year, continued a strong week that saw him topple world number three Casper Ruud on Thursday.