Alex de Minaur won the final four games of the first set to gain momentum and went on to post a 7-5, 6-4 victory over 11th-seeded Cameron Norrie on Tuesday in the first round of the National Bank Open in Toronto.
The 24-year-old de Minaur had 17 winners and just 10 unforced errors while advancing in windy conditions.
He's also a hot player after advancing to the final in Los Cabos last week before losing to Stefanos Tsitsipas.
"I'm just finding my game," said de Minaur, who has won seven career ATP titles. "I've always thought I've had this level, and now I've just put a couple of good matches together and that gives you confidence. So you build on that, and hopefully we can keep it going."
Norrie of Great Britain had 22 winners and 18 unforced errors in the one-hour, 43-minute match.
In the second round, de Minaur will face Canadian wild card Gabriel Diallo, who was a 7-6 (4), 7-5 winner over Daniel Evans of Great Britain. Diallo and Evans each had eight aces in the match.
In another first-round upset, Australia's Aleksandar Vukic rolled to a 6-2, 6-3 victory over 14th-seeded Borna Coric of Croatia. Vukic had a 23-11 edge in winners.
Germany's Alexander Zverev, the No. 13 seed, outlasted Tallon Griekspoor of Netherlands 6-4, 7-6 (3). Zverev smacked 12 aces.
Britain's Andy Murray knocked off Italy's Lorenzo Sonego 7-6 (3), 6-0, while Ugo Humbert of France rallied for a 4-6, 6-3, 6-4 triumph over Nicolas Jarry of Chile.
Americans Sebastian Korda, Mackenzie McDonald and Marcos Giron all won their matches.
Korda cruised to a 6-3, 6-2 victory over Argentina's Tomas Martin Etcheverry; McDonald was a 6-3, 6-4 winner over Russia's Aslan Karatsev and Giron recorded a 7-6 (4), 7-6 (6) win over Finland's Emil Ruusuvuori.
Other first-round winners included Australian qualifier Max Purcell and American Ben Shelton. Purcell captured a 6-4, 6-4 upset of No. 10 seed Felix Auger-Aliassime of Canada, while Shelton topped Spain's Bernabe Zapatas Miralles 7-6 (1), 6-4.
Third-seeded Norwegian Casper Ruud beat Jiri Lehecka 7-6 (6), 6-4 in a second-round match on Tuesday.
—Field Level Media