The 24-year-old from Vancouver came up against Novak Djokovic in the first round of the Dubai Tennis Championships on Tuesday, dropping a 6-4, 6-4 decision to the top-ranked Serb.
Djokovic was playing for the first time since he won his fifth Australian Open at the beginning of the month.
"It's my first match since the Australian Open final so I'm still looking for that rhythm on the court," Djokovic said. "I managed to stay mentally tough, patient and as soon as I got into the rallies I had a better chance of winning."
Also, third-seeded Andy Murray was given a workout by Gilles Muller of Luxembourg before securing a 6-4, 7-5 win, and fourth-seeded Tomas Berdych, a finalist at Dubai the last two years, beat Jeremy Chardy of France 7-6 (2), 6-4.
It took Muller 30 points to finally hold serve in the third game of the first set.
"I made him work very hard on his service games," Murray said. "That was something I wanted to try to do from early on."
In the final game of the first set, Murray served three aces, three double-faults, and saved a break point before winning the 16-point game.
Berdych started off with a 2-0 lead, but Chardy rebounded and played solid tennis until Berdych raced to a 5-0 lead in the tiebreaker.
"I made it complicated a bit more than usual," Berdych said. "Not every day it's going to be perfect. We don't have to be perfect."
The win put Berdych one victory away from claiming 500 match wins in his career.
Other winners included Marcos Baghdatis, sixth-seeded Feliciano Lopez, seventh-seeded Roberto Bautista Agut, Sergiy Stakjovsky and Simone Bolelli.
— With files from The Canadian Press.