Alex Morgan scored in the last minute of extra-time as the USA dramatically defeated Canada 4-3 to seal a place in the Olympic women's football final.
Christine Sinclair scored a superb hat-trick as Canada led three times.
But Megan Rapinoe scored direct from a corner and later with a fierce strike before Abby Wambach converted a penalty to make it 3-3.
And with a penalty shoot-out looming, the defending Olympic champions struck through Morgan's late header.
It was a classic game of football at Old Trafford, worthy of any occasion, and gives the US the chance to avenge their penalty shoot-out defeat by Japan in the final of the 2011 World Cup.
The US, three-times Olympic football gold medallists, tore into their near neighbours from the opening whistle and were soon creating chances, with Rhian Wilkinson blocking a strike from Carli Lloyd and Rapinoe shooting wide from long range.
Canada coach John Herdman had apparently angered the US players after suggesting that they "are very good" at using illegal tactics and it looked as though Pia Sundhage's team had a score to settle.
However, they could not prevent Sinclair from putting the Canucks ahead with a stunning goal.
The Canada skipper collected a pass from Melissa Tancredi and wrong-footed Kelley O'Hara before slotting the ball beyond Hope Solo from eight yards for her 141st international goal.
Solo was soon back in action again, denying Sophie Schmidt, before the US twice went close with headers.
An unmarked Morgan failed to hit the target from a Rapinoe free-kick and Wambach also missed the target with a good opportunity.
The US levelled after the restart, although the goal was in part down to some poor Canada defending.
Sinclair and Lauren Sesselmann were both close to the goal-line but neither could get a touch to Rapinoe's corner, which squeezed in at the near post.
Canada responded, with Sinclair scoring a superb header to kick off a burst of three goals in six minutes.
Rapinoe made it 2-2 with a blistering strike from the edge of the box that struck one post and thundered across the face of goal before nestling in the net.
Sinclair wasn't finished yet and headed Canada back in front for a third time from a corner to complete her hat-trick.
It seemed as though a remarkable spell of play had drawn to a close but more was to come after Canada keeper Erin McLeod was penalised for holding the ball inside the area for more than six seconds.
An indirect free-kick was awarded, which Rapinoe eventually struck towards goal. It hit the arm of the unfortunate Sesselmann as she tried to block the ball and referee Christiana Pedersen awarded a spot kick that Wambach converted.
Wambach, whose penalty took her level with Sinclair on 143 international goals, should have snatched a late victory but could not quite slot home at the far post after stretching to reach Morgan's cross.
Both teams tired considerably during extra-time, but Wambach almost scored a decisive goal after 118 minutes only to see her header hit the crossbar before Morgan did snatch the most dramatic of victories for her team.
The US will now face Japan on Thursday at Wembley, hours after Canada play France in Coventry in the bronze medal match.