MASON, Ohio -- Canada's Felix Auger-Aliassime has made an early exit at the Western & Southern Open.

Serbia's Miomir Kecmanovic upset the 19-year-old from Montreal 6-3, 6-3 in the first round of the ATP Tour 1000 Masters event on Monday.

Kecmanovic is ranked 58th in the world, while Auger-Aliassime is 21st.

Coming off a run to the third round at his hometown Rogers Cup last week, Auger-Aliassime didn't come close to matching that result at the second Masters event in a row.

Auger-Aliassime had 31 unforced errors, 22 more than Kecmanovic. That was a bigger gap than in winners, with Auger-Aliassime having 21 and Kecmanovic putting up nine.

Auger-Aliassime also had 10 double faults, nine more than Kecmanovic. The Canadian didn't have one break-point opportunity in the match.

Despite the loss, it's possible Auger-Aliassime will be the highest-ranked Canadian for the first time in next week's rankings. He's set to overtake Milos Raonic of Thornhill, Ont., who is out this week after suffering a back injury in the second round against Auger-Aliassime last week in Montreal.

Denis Shapovalov of Richmond Hill, Ont., ranked 34th, caught a break Monday when his scheduled first-round opponent, No. 10 seed Fabio Fognini of Italy, withdrew. Instead, Shapovalov will face lucky loser world No. 43 Joao Sousa of Portugal on Tuesday.

No Canadian women are in the draw. Bianca Andreescu of Mississauga, Ont., withdrew after winning the Rogers Cup on Sunday in Toronto.