Yuki Ogimi scored in the fifth minute for Japan, which secured first place in Group C and a spot in the knock-out stage of the tournament.
Ogimi's close-range shot went crossbar and in after the ball had been deflected towards the open net.
Ecuador finished group play with three losses, being outscored 17-1 in the process.
Cameroon will also advance from Group C after defeating Switzerland 2-1 at Edmonton's Commonwealth Stadium.
Madeleine Ngono Mani came off the bench to score one of two second-half goals for the African nation, which wrapped up group play with two wins and one loss.
Ana Maria Crnogorcevic gave the Swiss a 1-0 lead in the 24th minute. Gabrielle Onguene tied the match for Cameroon in the 47th and Mani put home the winner in the 57th.
Switzerland finished with one victory and two losses in Group C, with its only win against Ecuador.
Abby Wambach scored just before halftime as the United States defeated Nigeria 1-0 at B.C. Place Stadium in Vancouver to take top spot in Group D.
The American captain flicked her boot at a Megan Rapinoe corner kick in the 45th minute, slicing the ball home to give the U.S. the only offence it would need.
The U.S. finished group play with two wins and one draw, while Nigeria wrapped up round-robin action with one draw and two defeats.
Australia secured second spot in the group after tying Sweden 1-1 in Edmonton.
Lisa De Vanna put the Aussies ahead in the fifth minute. Sofia Jakobsson, however, responded only 10 minutes later to give the Swedes their third draw in as many matches.
Australia finished the group stage 1-1-1.