* Canada's Agosta celebrates birthday with three-point night
* Canada, U.S. on gold-medal collision course in Sochi (Adds quotes and details)
By Frank Pingue
SOCHI, Russia, Feb 12 (Reuters) - Canada edged the United States 3-2 in a clash between the women's ice hockey heavyweights on Wednesday, giving the three-time defending Olympic champions a psychological edge ahead of an expected gold medal matchup at the Sochi Games.
The marquee game of the preliminary round offered what many have come to expect from the sport's two superpowers - an intense, back-and-forth, physical battle played at a high tempo that went down to the wire.
Trailing 1-0 early in the third period, Canada got two quick goals from Meghan Agosta, who was celebrating her 27th birthday, and Hayley Wickenheiser to pull ahead before enduring a frantic finish to seal the win and top spot in Group A.
"It's an unbelievable feeling," said Agosta, who finished with two goals and an assist. "I didn't go out there thinking I'm going to score on my birthday, but it wasn't just about me. We won as a team."
Canada looked headed for a comfortable finish after Agosta scored her second of the game to give her team a two-goal cushion with about five minutes to play.
But the Americans pulled their goalie in favour of an extra attacker and the move paid off as Anne Schleper scored with 65 seconds left.
Canada then took a penalty for having too many players on the ice but the Americans, still playing with an empty net, were unable to make advantage count.
"We've taken some hits and we'll come back from it," said U.S. forward Hilary Knight. "Unfortunately we haven't had the greatest puck luck today but we'll come back a stronger team the next time."
The loss was the first of the tournament for the United States but they will also advance directly to the semis as they finished second behind Canada in the group.
Since women's ice hockey was added to the Olympic programme at the 1998 Nagano Games, Canada and the United States have accounted for all four gold medals.
The Sochi Games is debuting a new format aimed at avoiding the embarrassing routs at previous Olympics that have put the sport's Olympic future in doubt.
(Editing by Peter Rutherford)