Pospisil, ranked 129th in the world, was rewarded for his aggressive approach, rushing the net whenever the opportunity arose and pouncing on Murray's second serve.
"I knew I was a long shot. I've played Andy four times and didn't win a set," the 26-year-old told Tennis Channel.
"I felt like I had the ability to (win) but to actually go through is a whole new thing. I tried to bring different tactics ... versus the other times I played him.
"I didn't want to give him the same look each time. I wanted to put pressure coming into the net, using my strength, which is my ability at the net and serving well."
Pospisil joked that his lowly current world ranking was due to a "mid-life crisis" that saw him endure a lean 2016, after he had made the Wimbledon quarter-finals in 2015.
Earlier, Italian Fabi Fognini won a battle of expectant fathers when he beat Jo-Wilfried Tsonga 7-6(4) 3-6 6-4.
Unseeded Fognini survived a first-set tiebreak and a tense final set before upsetting the seventh-seeded Frenchman in a match that stretched nearly two hours and 30 minutes in the blazing afternoon sun.
"I am happy about my performance. It's a good victory for sure," Fognini told Tennis Channel after beating Tsonga for the first time in five career meetings.
"Today was really hot so the ball was bouncing a lot. I love playing with sun and good weather."
Fognini considered himself fortunate even to make it to the second round.
The Italian dropped the first set to love and was down 5-2 in the second set of his first-round encounter with Russian Konstantin Kravchuk, before roaring back to win 0-6 7-5 6-4.
"It is a crazy sport," Fognini said.
Fognini's wife, 2015 U.S. Open champion Flavia Pennetta, is expecting a child in late May, while Tsonga is also set to become a father next month.
In another upset on Saturday, Japanese world number 70 Yoshihito Nishioka beat Croatian veteran Ivo Karlovic 6-4 6-3, but seeds Dominic Thiem, David Goffin and Tomas Berdych won their matches to advance.
(Reporting by Andrew Both in Cary, North Carolina, editing by Gene Cherry/Peter Rutherford)
Share
