USA are through to the Women’s Olympic Football Tournament final and an opportunity for revenge against Japan, after overcoming Canada 4-3 following extra time in a sensational semi-final at Old Trafford in Manchester. Alex Morgan scored the winning goal in added time of extra time with a terrific header from a Heather O’Reilly cross to conclude an outstanding match, which the Americans had not led until the final seconds, and ensure her side maintained their record of reaching every Olympic final since the women\'s tournament\'s inception in 1996. Christine Sinclair bagged a hat-trick, taking her tally at London 2012 to six goals and putting Canada ahead on three separate occasions, only for Megan Rapinoe, twice, and Abby Wambach to equalise and keep USA hopes alive. The Americans will now face reigning world champions Japan, who beat USA to win the FIFA Women’s World Cup in 2011, in the gold medal match at Wembley on Thursday, while Canada have the chance to earn a bronze medal against the other beaten semi-finalists, France, in Coventry earlier that day. USA had not looked back since recovering from a two-goal deficit to beat France in their opening match of the tournament and they were dominant throughout the opening twenty minutes. Determined to retain a clean sheet, Canada were aggressive in the tackle and for all their lack of possession, restricted their neighbours to half-chances as they weathered a storm of attacks. When a goal for USA seemed inevitable, Canada delivered a sucker-punch on 22 minutes. Driving towards the American goal, Melissa Tancredi found team-mate Sinclair with a precise pass. Sinclair continued her momentum from joining the counter-attack to run into the box, skilfully elude a defender and maintain her composure to slide a finish past Hope Solo. Suddenly USA were rattled and the Canadians could have doubled their advantage five minutes later. Again it was a swift counter-attack which provided the chance, this time for Sophie Schmidt, who guided a header towards goal which Solo handled well. Pia Sundhage’s team reacted impressively and Morgan was involved in key moments twice in quick succession. Firstly she was found by an inswinging Rapinoe free-kick but her glancing header drifted agonisingly wide of the far post. Then, not for the first time in the opening period, Morgan was released with space on the right hand side and her cross was aimed for strike partner Wambach, who connected with a strong header which finished off target. If clear chances were minimal during the first 45 minutes, the floodgates opened when the second half began, as Canada and USA shared one of the most pulsating halves in the history of women’s football. Rapinoe’s delivery from set-pieces and open play was a significant feature of the first half and, nine minutes after the restart, the 27-year-old helped USA to level the score. Her whipped corner-kick caused havoc among the Canada defence and squeezed in at the near post to make it 1-1. Sinclair and Tancredi have been one of the star duos of London 2012 and the pair combined again in the 68th minute to regain the lead for Canada. The latter made room for herself on the left wing and a pinpoint cross found her colleague, who directed a header back towards goal and past Solo’s reach. The goal was the catalyst for a stunning period of football and perhaps the most exciting of the tournament so far. After providing cross after cross, Rapinoe chose a more direct route two minutes after USA fell behind for the second time, smashing a brilliant shot off the post and in to equalise. Canada simply refused to give in, however, and, with the third goal in five thrilling minutes, Sinclair claimed her hat-trick and put John Herdman’s team ahead for the third time. The 29-year-old rose highest to reach a Schmidt corner from the left side and beat Solo with another header. With ten minutes left on the clock, USA clawed their way back into the match yet again. Having scored in each of USA’s matches at the tournament to date, Wambach again wrote her name on the scoresheet, converting apenalty after the referee awarded a spot-kick for handball from a Rapinoe free-kick. Wambach could have claimed a winner when found at the backpost by Morgan but her effort went wide, before Schmidt ran clear of the American defence only to be thwarted by Solo as extra time was required to decide the match. The pace showed no sign of slowing down during the additional period, but the closest either side came was in the 118th minute, when Wambach’s looping header bounced back off the crossbar. Penalties seemed inevitable as the remaining seconds disappeared, until Morgan had her moment.