Great Lakes jumped out to a 1-0 lead early on Saturday when James Outman hit a solo home run.
The game remained 1-0 until Corey Joyce was hit by a pitch with the bases loaded to score Andre Lipcius which gave the Whitecaps their first run of the game, making the score 1-1.
The score remained 1-1 until the walk-off hit by Torkelson.
Reliever Chavez Fernander picked up the victory, tossing two clean innings and striking out three batters.
Torkelson and Joyce each had one RBI to lead the Whitecaps offense on the night which was held to just five hits in the victory.
The Whitecaps are now 4-6 overall on the season and will wrap up their series with Great Lakes on Sunday with first pitch scheduled for 2 p.m.