Jaroslav Kulhavy of the Czech Republic won Olympic gold with a sprint finish at the end of the London 2012 men's mountain bike race at Hadleigh Farm.
The 2011 world champion had enough strength to hold off Nino Schurter of Switzerland in one hour 29 minutes 07 seconds, with Italy's Marco Fontana third, 25secs adrift.
Julien Absalon of France, the 2004 and 2008 champion, did not finish after falling down the field following a puncture.
Britain's Liam Killeen, who was fifth in Athens and seventh in Beijing, crashed out on the second of seven laps, tumbling at Deane's Drop and suffering a suspected broken left ankle.
The 30-year-old from Malvern was transferred by ambulance to hospital for surgery.
Germany's Robert Forstemann, who entered the mountain bike event to exploit a loophole and take a place on the velodrome track, did not even start the race, which was seven laps of a 4.7-kilometre route, carved into an Essex hillside overlooking the Thames estuary.
Adrien Niyonshuti, a survivor of the 1994 genocide, did start for Rwanda, while Killeen began in 25th position on the grid and was never in contention.
Absalon lost touch with Schurter, who won four rounds and the overall World Cup series title this season, and Kulhavy on the first lap.
Schurter, Kulhavy and Fontana established a narrow lead at the end of the opening circuit, with Jose Antonio Hermida of Spain leading the chase.
Killeen tumbled down Deane's Drop, a steep boulder section, and was joined in failing to finish lap two by Absalon.
South Africa's Burry Stander and Hermida bridged the gap at the end of the third lap to join the three leaders.
Kulhavy took the lead on the fifth lap and stretched the group with the relentless pace, opening up a narrow lead over Schurter and Fontana with two laps to go, with Stander and Hermida losing contact.
Kulhavy and Schurter were vying for the win, with Fontana dropped in the closing stages of the final lap.
Schurter moved to the front but Kulhavy rounded his rival to triumph.