In the same tournament, he claimed the scalp of world No 2 Rafa Nadal and Del Potro, and later that year, he reached the US Open fourth round, a feat not seen by a male so young at a grand slam since Michael Chang in 1989.
That debut professional season set an impossibly high benchmark, as he rocketed from world No 250 to the cusp of the top 50.
With the accompanying hype, expectation and scrutiny, those levels can be hard to maintain and many players have struggled in their sophomore seasons. But not Shapovalov.
He beat some impressive names in 2018, such as Kei Nishikori, Sam Querrey, Tomas Berdych and Fabio Fognini, and reached the last four at the Madrid Masters, becoming the youngest semifinalist in the event's history.
"[Madrid] showed it wasn't a fluke in Montreal, and at the same time, it showed me that, too," said Shapovalov.
"I had my doubts two years ago and at the beginning of last year, if Montreal was just a one-time thing, or if I could ever get my game back there.
"After that [Madrid] result, it gave me that sense of calmness and security that I am able to play at this level, able to beat the top guys. Ever since then, I feel much more comfortable on tour."
He also appears grounded and genuine, given his profile. He's engaging and sincere in media interviews, and seemed like just another teenager yesterday, as he joked around at a sponsor's opportunity and recalled meeting the Breakers in Auckland last year.
"It's natural for me to stay humble," said Shapovalov. "I grew up in that environment and that's the person I am. I come from a humble family and have a supportive team around me. They keep me motivated, but also if something is going on, they step on me and make sure I stay grounded."
There's a plethora of young talent on the ATP tour, as well as the hardened veterans and big names, but Shapovalov looks well positioned to make an even bigger impact in 2019.
"Honestly, I think I'm in an unbelievable spot," said Shapovalov.
"Twenty-seven in the world at 19-years-old. Last year, it's an extremely difficult year for any player. Two years ago, I had a breakthrough, hit top 50 in the world, and last year was about defending that.
"Not only did I defend it, I raised my ranking - almost cut it by half - and on top of that, I had my sense of calmness.
"I feel like my game belongs with these guys; my game is where my ranking is. So I feel really motivated this year to keep going forward, keep getting better, keep on going"
Shapovalov faces world No 44 and 2017 Auckland finalist Joao Sousa in the first round.
Other matches see four-time champion David Ferrer take on classic regular Robin Haase, while former Kiwi Cameron Norrie has drawn Frenchman Benoit Paire.
New Zealand No 1 Rubin Statham received a late wildcard yesterday and is pitted against highly-rated South Korean Hyeon Chung, the world No 25 who reached the semifinals in Melbourne last year.
• Two-time Wimbledon finalist Tomas Berdych, who was set to make his first visit to Auckland, has pulled out of the tournament after reaching the final of the Doha ATP event.
Berdych, who reached a career-high ranking of four, was one of the biggest names in the field after being granted a wildcard by tournament director Karl Budge last year.
It's a disappointment for the event and fans, but also a reality of tennis, especially for the ASB Classic.
Berdych's place is the main draw is taken by former top New Zealand junior Norrie, who now plays under the British flag.
The world No 90 lived in Auckland from an early age, after his parents emigrated from South Africa.
He was an outstanding local prospect, reaching the top 10 in the world as a junior, but struggled to gain much support or funding from Tennis New Zealand at the time and switched allegiance to Britain just before his 17th birthday, turning professional in June 2017.
