The Blue Jays' No. 19 prospect belted homers off three different pitchers and drove in five runs to power the Triple-A Las Vegas 51s to an 11-1 romp over Tucson.
Sierra, who had not gone deep since May 7, recorded the eighth three-homer game in the Minor Leagues this season and the first in the Pacific Coast League.
"I'm really happy [with tonight] because I went a month without one," Sierra said through a translator. "I was just waiting for it. I'm happy to break out in this way."
The 23-year-old outfielder flied to right in the second inning, but none of his subsequent fly balls would be playable.
In the fourth, Sierra deposited an 0-1 slider from starter Bear Bay over the right-field fence for his first homer in 21 games. He sent a 1-0 fastball from Jason Ray over the same fence an inning later to extend Las Vegas' lead to 7-1.
After grounding out in the seventh, Sierra found himself with one last at-bat in the ninth. Facing Major League veteran Chris Haney with a runner on second, he pulled a 1-1 offering to left for his ninth homer of the season.
"I've never had a game like this one," Sierra said. "I'm just really happy to have a good game for the team, to help the team win."
The native of the Dominican Republic raised his slugging percentage 50 points to .460 and is third on the PCL's most offensive team with 31 RBIs.
It was the right kind of start to June for Sierra, who batted .264 with six extra-base hits in May.
"I worked hard with our hitting coach, Chad Mottola, in the cage, making a lot of adjustments," he said. "I was feeling good from the first at-bat [tonight] and had a good game because of the adjustments we've made."
Sierra was an Eastern League midseason All-Star at Double-A New Hampshire last year, hitting .277 with 18 homers and 67 RBIs in 133 games.
It also was a big night for Toronto's other outfield prospect, Anthony Gose. The Blue Jays No. 2 prospect went 4-for-5 with a double and four runs scored, extending his hitting streak to 16 games. He's 32-for-69 (.464) during that stretch to hike his average to .307.
No. 16 prospect Adeiny Hechavarria chipped in three RBIs on a 2-for-4 night, while Adam Lind went 3-for-3 and drove in a run.
Las Vegas starter Bill Murphy (1-2) allowed a run on three hits over six innings for his first win since Sept. 1, 2008.