Defending gold medalist Canada has clinched the top spot in pool play by edging the United States 2-1 in an early Olympic showdown between the dominant powers in women's hockey.

Meghan Agosta and Sara Nurse each scored in the second period, and Genevieve Lacasse made 44 saves. Canada and the United States are the only countries to ever win gold at the Olympics.

Lacasse stopped Hilary Knight at the post inside the final 90 seconds. Brianne Decker hit two posts, the second in the final seconds, before punching, pushing and shoving. Officials reviewed the final play and ruled no goal.

The Canadians also had two goals disallowed, the second midway through the third for Haley Irwin kicking the puck in off her left skate.

The Americans have not taken home gold since 1998, while Canada is here looking for a fifth straight.