Women's World Cup holders Japan launched their bid for Olympic glory with victory over Canada in their opening Group F encounter at the City Of Coventry Stadium.
First half goals from Nahomi Kawasumi and Aya Miyama put Japan in command before their opponents staged a spirited second half comeback.
Japan had strong claims for a penalty rejected after Kaylyn Kyle appeared to push Mizuho Sakaguchi in the back.
But Japan, who finished fourth in the 2008 tournament, took command with two goals in 11 minutes.
Kawasumi broke the deadlock after 33 minutes when she seized onto a back heel from Shinobu Ohno inside the box and bent the ball past Canadian keeper Erin McLeod.
A minute before the break Miyama made it 2-0. McLeod failed to deal with a cross from Aya Sameshima and Miyama headed into an empty net.
Japan continued to look the more threatening and Lauren Sesselmann cleared off the line from Homare Sawa after 51 minutes.
But Melissa Tancredi reduced the arrears four minutes later when she turned home a low centre from Rhian Wilkinson.
McLeod kept out a dipping drive from Yuku Ogimi who also headed over when well placed as Japan re-asserted their authority.