The Spaniard became the first unseeded player to win the Montreal Masters tournament since Guilhermo Canas in 2002 after weathering an early storm to shock the eighth seed 3-6 6-3 6-3 on Sunday.
"It's an amazing feeling to be a Masters 1000 winner," Carreno Busta, who claimed his seventh tour-level title, said post-match.
"It's the best title of my career for sure and I don't know how I'm feeling in this moment.
"I know that during all the week we worked very hard, also the weeks before. It's very important to be very positive all the time. It's not my best season this year. I lost some matches that probably other seasons I didn't lose, but I just tried to continue believing in my team, in myself and in my game."
Having come through a gruelling semi-final encounter with Brit Daniel Evans to reach his first ATP 1000 final in singles, the Tokyo 2020 bronze medallist struggled to deal with his opponent's impressive slew of aces in the first set, and saw his serve broken in the sixth game.
But a ruthless start to the second set saw the 23rd-ranked Carreno-Busta break early, racing out to a 3-0 lead and holding his nerve to keep the gap to his Polish opponent, who was chasing a second ATP 1000 crown.
World No.10 Hurkacz attempted to rally with a fine start to the third set, but another loss of serve effectively stalled his momentum and Carreno-Busta was able to take the victory.
"He definitely was playing really amazing this week,"Â Hurkacz said.
"I congratulate him because that's his biggest success so far. He definitely deserved it."
The result marks a much-needed boost for 31-year-old Carreno-Busta, who suffered first-round exits at the French Open and Wimbledon after making the last-16 in Australia, with the US Open set to start later this month.
With Reuters.
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