The winning goal came after half an hour, as Takahiro Ogihara curled in a corner which was missed by the Spanish defence, allowing Borussia Mönchengladbach's Yuki Otsu (pictured above) to slide home past David de Gea.

Spain's troubles were worsened just before half time as Kensuke Nagai tried to break free on goal but was hauled down by Iñigo Martínez.

The referee sent off the Real Sociedad player, leaving his team a man and a goal down at the break.

Spain poured forward in the second half in search of an equaliser but struggled to make anything of their possession.

Instead it was Japan who threatened most, however, Hiroshi Kiyotake missed their most promising chance when he fired just wide.

Kiyotake is checked by Alvaro Dominguez of Spain during the men's football first round group D match of London 2012

Japan almost made it 2-0 again moments later, and continued to look more likely to score on the counter attack than Spain were for all their pressing.

Hotaru Yamaguchi had their best chance, in the dying moments, but he failed to convert when it seemed easier to score.

Fortunately for Japan, by then Spain had resorted to uncharacteristically lumping long balls forward in search of an equaliser, with the likes of Juan Mata and Ander Herrera running out of ideas.

Luis Milla's side can at least console themselves with one positive omen.

In 2010, Spain won the World Cup after losing their opening match, 1-0 to Switzerland, in similar circumstances.

The Spanish face Honduras and Morocco in their final two matches.

Both sides looked good this afternoon as they drew 2-2 at the same venue.

Barrada of Morocco celebrates after scoring his team's first goal of London 2012

In an open game, Morocco struck early on as Abdelaziz Barrada showed why he is so highly rated with a superb volley.

Jerry Bengtson levelled things up for Honduras just after half time before he slotted home a penalty.

Moments later Morocco's Zakaria Labyad lobbed the ball over Jose Mendoza to level the scores again after a flowing move.

The result will give both teams hope, although that will have dissipated somewhat after watching Japan's heroics.

South Korea also started well, but had to settle for a 0-0 draw with group favourites Mexico in their opening match at Newcastle's St James's Park.

Giovani dos Santos was surprisingly left on the bench as Mexico showed precious little sign of their usual fluidity.

Dos Santos (C) shoots at goal during the London 2012 Olympic men's football match between Mexico and South Korea at St James' Park

Instead South Korea spurned a number of chances, most notably when Koo Ja-Cheol fired against the crossbar before heading narrowly wide with 10 minutes remaining.

Elsewhere in the group B, Gabon and Switzerland also drew at St James' Park.

Admir Mehmedi put the Swiss ahead with a penalty but missed a golden chance to make it 2-0 after 20 minutes.

That proved costly as Gabon fought back with Pierre Emerick Aubameyang slotting in an equaliser, while Switzerland finished with 10 men after Oliver Buff was sent off.

Brazil beat Egypt 3-2 but almost let a comfortable advantage slip in their opening game at the Millennium Stadium in Cardiff.

Rafael put the Seleção in front with a left foot strike before a flowing move was finished off by Leandro Damião for goal number two.

Santos star Neymar then made it 3-0 before half time as Mano Menezes' side threatened to run riot.

However, goals from Mohamed Aboutrika and Muḥāfaẓat al Gharbiyya in the second period almost earned the Egyptians an unlikely comeback.

Baga (R) vies for the ball with New Zealand’s Kosta Barbarouses at The City of Coventry Stadium

The other game in Group C saw Dmitry Baga's (pictured above, right) strike earn Belarus a victory over New Zealand in Coventry.

Britain drew their first game at the Olympics in over 50 years when they tied 1-1 with Senegal at Old Trafford, as Craig Bellamy's first half strike was cancelled out by an equaliser from Moussa Konaté.

The day's other match saw Uruguay come from behind to beat the United Arab Emirates at the same Manchester ground.

Ismail Matar put the gulf nation into a shock lead, but a free kick from Gaston Rodriguez and a goal from Nicolás Lodeiro gave the South Americans a winning start.

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