Japan's World Cup-winning women got their Olympic campaign off to a successful start with a 2-1 victory over Canada.
Nahomi Kawasumi's powerful finish put Japan ahead before Aya Miyama headed in a second after a defensive mix-up.
Melissa Tancredi pulled one back for Canada from close range, but they were unable to find an equaliser.
In Group F's other match at the City of Coventry Stadium, Sweden hammered Olympic debutants South Africa 4-1.
The Swedes put on a show against their African opponents as they fully illustrated the gap between sides ranked fourth and 61st respectively in the Fifa rankings.
Sweden had already hit the crossbar twice before captain Nilla Fischer gave them a seventh-minute lead with a shot from the edge of the area that deflected in off Refiloe Jane.
Lisa Dahlkvist side-footed home a Marie Hammarstrom centre to double Sweden's lead before Lotta Schelin slipped the ball past South African keeper Roxanne Barker to make it 3-0 just 60 seconds later.
Portia Modise scored arguably the goal of the game - chipping Swedish keeper Hedvig Lindahl from just outside the centre circle - to reduce the arrears on the hour mark.
However, three minutes later Schelin converted a near post cross from Dahlkvist for her second goal and reassert Sweden's utter dominance.
The next round of matches, on Saturday, sees Sweden face Wednesday's other victorious side, Japan.
The Japanese - who surprisingly beat the United States in last year's World Cup final - deserved their win over Canada, but were made to work for it.
Miyama was a key figure in a dominant first half display, which saw her set up Kawasumi's first goal with a neat backheel before scoring the second.
However, they were made to work harder after the break by a spirited Canada, who next face South Africa in Saturday's other Group F match.