UCLA's Lauren Cheney scored both goals in the win for the U-20s, who were coming off a 3-2 loss to Mexico, also fielding its full national team, in their final group game. Cheney was suspended for that match after being red carded in the USA's win over Argentina
The U.S. team was outshot by Canada, 15-6, but got a goal in both halves from Cheney, then fended off a late rally to record the win. Kara Lang, Cheney's UCLA teammate, scored with two minutes left for Canada.
Canada lost to Brazil, 7-0, in their group finale.
The U.S. men's team was knocked out of medal contention when it fell to Mexico, 2-0, in its final group game.
WOMEN'S SOCCER SEMIFINAL
July 23 in Rio de Janeiro
USA 2 Canada 1. Goals: Cheney 18, 77; Lang 88.
USA -- Naeher, Taylor, Marshall, Wilmoth, Fountain, Enyeart (Wright, 60), Heath, Edwards, Nogueira, O'Hara (McDonald, 85), Cheney.
Canada -- LeBlanc, Booth (Vermeulen, 46), Tancredi, Andrews, Hermus, Neil, Matheson, Thorlakson, Wilkinson, Lang, Sinclair.
Referee: Ricardo Cerdas (Costa Rica).