Alexei Popyrin has capped off a stunning run to become the first Australian to win ATP Masters 1000 title since Lleyton Hewitt 21 years ago.

The 25-year-old defeated sixth-ranked Andrey Rublev 6-2 6-4 in the Montreal final to complete the biggest triumph over his career.

World No.62 Popyrin stayed focused as Rublev went into a trademark meltdown as he lost his chance for a second Masters trophy this season after winning Madrid.

Rublev screamed at his errors, kicked a towel holder and beat himself up mentally throughout as Popyrin duplicated the 1000-level success last achieved by compatriot Hewitt at Indian Wells in 2003.

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Rublev was seen by the doctor after the third game of the second set and given tablets, with the player motioning to his stomach as a possible source of his discomfort.

Popyrin’s ranking is set to soar to a career-high of No.23 in the world, meaning Australia could have as many as three seeded mens players for the US Open.

Tennis commenators called it one of the biggest shocks in recent memories as Popyrin’s third career title came at the prestigious Masters event, worth $US6,795,955 ($A10 million) in prizemoney including $1,049,460 ($A1.5 million) to the winner.

The only other Aussie to reach a Canadian final was Patrick Rafter in 2001, who lost to Romanian Andrei Pavel.

Popyrin, who turned 25 last week, is the fourth from his nation to win at this level, following Rafter (1998 Toronto, 1998 Cincinnati), Mark Philippoussis (1999 Indian Wells) and Hewitt (2002-2003 Indian Wells).

“This means so much, it means the world,” an emotional Popyrin said. “All the hard work we’ve put in over the last couple of years has paid off.

“Everyone around me has sacrificed so much of their lives for me. For me to win this for them is amazing.” Popyrin, who beat five top-20 opponents during his run to Canadian glory, said he treated match points like any other shot.

“I tried to focus on what I had to do on my serve,” he said. “My first two match points, I didn’t make a first serve, but on the third, I did what I felt I needed to do. I hit a pretty solid forehand to win it.” Rublev, who has boiled over several times this season on court and confessed to dealing with mental stress, got off to a poor start and took out his frustrations early through screaming, kicking a towel container and generally breaking down in tight moments.

His form in knocking out world number one Jannik Sinner in the quarter-finals was barely visible as he ran into an inspired Popyrin.

The Australian started the final on a tear, winning seven of the opening eight points as Rublev’s fragile temper began to fray.

Popyrin drove home his superiority with a double break as the seed double-faulted for a second time within minutes to lose serve.

Rublev annulled a set point in the six-minute seventh game to hold to 2-5. But Popyrin calmly finished off the opening set on his third chance.

The Aussie sent a sizzler down the line past Rublev to clinch a set where he twice saved double break points against his serve.

In the second set, Popyrin again began with a break as Rublev called for the doctor after the third game and was given tablets, presumably for the stomach problems which have plagued the locker room throughout last week.

Popyrin dropped his first service game as Rublev levelled for 3-all only to give it away a game later.

The seed was unable to make a late recovery, with Popyrin taking victory on his third match point with an unreachable winner.

Popyrin did have one small regret in victory.

“This is one of the few weeks where my girlfriend isn’t traveling with me… and I win the tournament,” he said. “I hope she comes to New York now.”