Last Updated: 27/07/12 9:07am
World and European champions Spain suffered a shock defeat to Japan in their opening fixture of the 2012 Olympic Games.
Honduras, Morocco, Mexico, Switzerland and South Korea picked up a point apiece as they began their gold medal campaign with stalemates, while much-fancied Uruguay claimed a hard-fought success.
Pre-tournament favourites Brazil prevailed in a five-goal thriller, Belarus claimed a memorable victory and Team GB made a stuttering start on home soil.
Spain slipped to a surprise defeat as Japan claimed a 1-0 win with a hugely impressive performance at Hampden Park.
Yuki Otsu's first-half goal was enough for three points but in truth the margin of victory could have been much greater as 10-man Spain struggled with the pace and pressure enforced by their opponents.
The 1992 Olympic champions were already 1-0 down when they had Inigo Martinez sent-off with five minutes remaining in the first half and failed to recover from their numerical disadvantage.
Elsewhere in Group D, a second-half double from Jerry Bengtson was not enough to hand Honduras only their second ever win in the Olympic Games as 10-man Morocco held on for a 2-2 draw at Hampden Park.
The Africans enjoyed the better of the opening period and went ahead seven minutes before half-time thanks to a sweetly struck volley from Abdel Barrada.
Honduras responded excellently after the break, though, and were level on 55 minutes when Bengtson tapped home Maynor Figueroa's shot from close range.
Bengtson then scored again from the penalty spot, but the lead only lasted two minutes before Zakaria Labyad equalised with a scooped effort that eluded Jose Mendoza.
Zakarya Bergdich was then shown a red card for kicking out at Mario Martinez with 19 minutes remaining but Honduras could not take advantage of their man advantage as the points were shared.
New Chelsea signing Oscar played a starring role as Brazil were forced to fend off a brave fightback from Egypt in their 3-2 win at the Millennium Stadium.
The midfielder set up Rafael and Leandro Damiao for the first two Brazil goals, before Neymar made it 3-0 at half-time in front of a crowd of 26,812, greater than the attendance at Wednesday's Team GB women's fixture against New Zealand.
The South Americans took their foot off the gas after the break and were punished as Mohamed Aboutrika and Mohamed Salah pulled goals back for Egypt, but it was not enough for the Africans.
Belarus also sit on three points in Group C as they marked their first appearance at a major tournament since gaining independence 21 years ago with victory over New Zealand at the City of Coventry Stadium.
An error of judgment by stand-in Kiwis keeper Michael O'Keeffe gifted Belarus midfielder Dmitry Baga the only goal on the stroke of half-time.
Substitute Raul Jimenez was denied an injury-time winner by the woodwork as Mexico and South Korea played out a 0-0 draw at St James' Park in Group B.
The striker clipped the outside of the post after being put through by Tottenham's Giovani dos Santos with the final whistle fast approaching.
Pierre Aubameyang denied 10-man Switzerland an opening Group B victory as Gabon claimed a hard-fought 1-1 draw.
The St Etienne striker cancelled out Admir Mehmedi's twice-taken penalty with a neat finish as the half-time whistle approached.
Luis Suarez had the last laugh on Old Trafford's boo-boys as Uruguay came from behind to beat United Arab Emirates in their Olympic opener.
Suarez's last appearance at the home of Manchester United involved the infamous handshake snub to Patrice Evra.
A sizeable section of those present clearly had not forgotten the negative headlines that accompanied Suarez last season and predictably, the Uruguay skipper was booed repeatedly.
When UAE skipper Ismaeil Matar gave his side a shock lead midway through the first-half, it seemed Suarez would have even more to bother him.
But Uruguay, highly fancied for the entire tournament, kept their nerve and after Suarez had been fouled 20 yards out, Bologna midfielder Gaston Ramirez curled the South Americans level.
Suarez was also involved in Uruguay's second, as he cut inside after collecting a pass from substitute Nicolas Lodeiro, who kept going and buried a clinical shot into the far corner.
The final game on a busy day of Olympic activity saw hosts Team GB held 1-1 by Senegal at Old Trafford.
Craig Bellamy fired Stuart Pearce's side into a first-half lead, but they were pegged back by Moussa Konate eight minutes from time.
DOB: 17/5/1956 Event: Boxing Medals: 1 gold Flag: USA
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