Japan upset Spain 1-0 on the first day of the men’s Olympic football tournament, while Brazil held on for a 3-2 victory over Egypt and host Britain had to settle for a 1-1 draw with Senegal.
Uruguay and Belarus also won on Thursday.
Japan pulled off the surprising win after outplaying gold-medal favourite Spain, which went a man down in the first half and couldn’t fight back.
Brazil got three first-half goals but nearly squandered the lead in the second, escaping with the victory to begin its quest for its first gold in Olympic football. Britain’s debut was spoiled by a late goal conceded in the draw with Senegal.
Japan got the winner in Glasgow when forward Yuki Otsu broke away from his marker during a corner in the 34th minute and the ball landed right at his feet for a simple tap-in past Manchester United goalkeeper David de Gea.
Spain was reduced to 10 men just a few minutes after the goal when centre back Inigo Martinez was sent off for a foul while trying to stop a Japanese player from scoring.
The loss comes as a blow for Spain’s under-23 team, which wants to win Olympic gold to add to the World Cup and European championship titles held by the country’s full national team.
The Olympic side has two more matches to turn it around, against Group D opponents Honduras and Morocco, which drew 2-2 in Newcastle.
In Cardiff, Brazil got goals from Manchester United’s Rafael in the 16th, Leandro Damiao in the 26th and Neymar in the 30th to earn a comfortable halftime lead before Egypt made it interesting with goals by captain Mohamed Aboutrika in the 52nd and substitute Mohamed Salah in the 76th.
Brazil leads Group C along with Belarus, which beat New Zealand 1-0 in Coventry with a first-half goal by Dmitry Baga.
At a nearly packed Old Trafford Stadium, Britain took the lead in the 19th after Senegal failed to clear a free kick into the box from captain Ryan Giggs. Fellow Welshman Craig Bellamy pounced on the loose ball, driving a shot into the ground that bounced to the left of keeper Ousmane Mane.
But Senegalese striker Moussa Konate ran on to a through ball that exposed Britain's defence fragility before chipping Butland from close range.
Uruguay posts win
Earlier in Manchester, medal contender Uruguay got a goal from substitute Nicolas Lodeiro in the second half to defeat the United Arab Emirates 2-1.
In Group B in Newcastle, Gabon rallied for a 1-1 draw against Switzerland and Mexico escaped with a 0-0 draw with South Korea.
The results: Men: Group A: UAE 1 lost to Uruguay 2; Great Britain 1 drew with Senegal 1. Group B: Mexico 0 drew with South Korea 0; Switzerland 1 drew with Gabon 1. Group C: Belarus 1 bt New Zealand 0; Brazil 3 bt Egypt 2. Group D: Honduras 2 drew with Morocco 2; Spain 0 lost to Japan 1.