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Video - Argentina victorious in Madison
British cyclists Bradley Wiggins and Mark Cavendish suffered disappointment in their bid for Madison glory as Argentina took a deserved gold medal.
The experienced Argentine pair of Juan Esteban Curuchet and Walter Fernando Perez won, with Spain taking silver and Russia bronze.
Wiggins was aiming to become the first British athlete since 1908 to win three gold medals at a single Olympic Games.
Britain came into the race as heavy favourites but finished joint eighth.
Wiggins had already won gold in both the men's individual and team pursuit and looked fatigued throughout.
The 28-year-old would have also surpassed American Burton Downing's all-time Olympic track cycling medal haul of six.
Cavendish, who claimed four stage wins in the 2008 Tour de France, returns home as the only member of Britain's track cycling team not to have won a medal.
The pair appeared out of sorts from the outset and suffered from a lack of allies as the field attempted to upset the reigning world champions.
The Madison is a 200-lap, two-man race where teams collect points in sprints held every 20 laps.
Argentina gained a lap on the field after the fourth sprint but when Wiggins tried to do so with about 60 laps remaining, he seemed to have run out of energy.
Cavendish attacked with 30 laps to go - a similar stage at which he did so in the world championships to devastating effect - but the 23-year-old, hoping to become the first athlete from the Isle Of Man to win an Olympic medal, was reeled in.
The 43-year-old Curuchet and Perez, 33, were world champions in 2004 and rode the race to perfection.
Spain and Russia both went on to lap the field, allowing them a cushion that proved decisive.
It means Spain's former seven-time world champion Joan Llaneras, who won the points race, will go home with a silver and a gold.
The 39-year-old previously won silver in Athens and gold in Sydney, both from the points race.