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8/15/2014 1:38 A.M. ET

Bryant's 40th homer is walk-off shot

Thursday night was Kris Bryant jersey T-shirt night at Triple-A Iowa's Principal Park. And the Cubs' No. 1 prospect celebrated his day in style, hitting a walk-off home run in the 12th inning to beat Las Vegas, 6-5.

The home run was Bryant's 40th of the season -- the most in the Minor Leagues. He is just the second player in the last five years to reach the mark, joining Rangers No. 1 prospect Joey Gallo, who did so last year.

Bryant had been hitless in four at-bats Thursday before coming to the plate in the bottom of the 12th inning to face Las Vegas reliever Chase Bradford. He had struck out three times when he was intentionally walked in the ninth inning.

But Bryant erased all of that in the 12th. Facing Bradford, he belted a deep fly ball over the fence in center field for a two-run home run. He finished the game 1-for-5.

Bryant, ranked No. 4 on MLBPipeline.com's Top 100 Prospects list, began the season with Double-A Tennessee. After a dominating first half (he was leading the Southern League in all three Triple Crown categories at the All-Star break), he was promoted to Iowa. In 122 games between the two levels, he is hitting .336/.442/.684 with 40 home runs and 15 stolen bases. He has scored 108 runs and driven in 103.

Teddy Cahill is a reporter for MLB.com. Follow him on Twitter at @tedcahill. This story was not subject to the approval of Major League Baseball or its clubs.