The Twins prospect hit a walk-off home run in the bottom of the ninth to give USA a 4-3 win over Australia, giving the United States the top seed in Group A heading into the World Cup final round.
USA will take on Venezuela on Tuesday in a rematch of the first game of the tournament. Venezuela won that game, 13-9, extra innings. Australia will face Cuba, Chinese Taipei will take on The Netherlands, and Canada will play Puerto Rico in other action Tuesday.
Before Plouffe's heroics, USA took a 2-1 lead in the bottom of the sixth inning on the ninth home run of the tournament by Rangers prospect Justin Smoak and an RBI by Rays prospect Jon Weber, but Australia took the lead back in the seventh, scoring one run on an error and another on a sacrifice fly.
In the bottom of the seventh, the U.S. tied the game at 3 on a Plouffe groundout that scored Royals prospect Tug Hulett from third.
Plouffe's blast in the final inning came with two outs and two strikes.
In other action Monday, Italy defeated The Netherlands, 7-6.
Jesse Sanchez is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.