Canadian defender Candace Chapman put her team ahead in the 27th minute when she sent a powerful low shot from outside the box to beat Argentine goalkeeper Vanina Correa.

"It is the first goal we have in Olympics," Chapman said. "It is really a special moment for me and teammates."

The North American women doubled the advantage in the 72nd minute when striker Kara Lang headed home a free kick from right wing. The 22-year-old also had a goal ruled out for offside in the first half.

Argentina pulled one back in the 84th minute. Substitute striker Ludmila Manicler shot home a cross from midfielder Mariela Coronel in a counter attack.

"The Canadian are much strong physically," Argentina coach Jose Carlos Borrello said. "We were just trying to show our skills."

The Canadian counted on their physical advantage by making long passes and fast attacks from the start. They controlled the situation since the first 20 minutes.

Canada's top scorer Christine Sinclair, with 93 goals in 122 international games, supplied a lot of assists to fellow strikers but failed to score.

Argentina had a good chance for scoring just nine minutes into the game when striker Mercedes Pereyra slammed a powerful shot at the edge of the box before Canadian goalkeeper Erin McLeod pushed out the ball with an excellent save.

The two teams are in Group E with Sweden and China. In the second round of the group, Canada will play against China on August 9 while Argentina will meet Sweden.