Great Britain's Shanaze Reade suffered Olympic disappointment for a second successive Games with a sixth-place finish in the women's BMX final.
A three-time individual world champion, Reade had a great lane draw but made her first bad start of the competition and her race was effectively over.
Mariana Pajon became only the second Colombian to win an Olympic gold medal.
Jamie StaffOlympic gold medallist and BBC cycling pundit
"Shanaze just didn't get the start she needed, it's as simple as that. It's the critical point of the race. Who knows what was going through her mind there at the start?"
New Zealand's Sarah Walker was a surprise silver medallist and Dutch teenager Laura Smulders won bronze.
The 20-year-old Pajon, world champion in 2011, was a class apart, winning all four of her races. For Reade, however, it was another opportunity missed.
She said: "At the moment, I'm pretty emotionless. I'm sure it'll sink in. I can't thank all these people enough for supporting me and I don't really know what to say. I just didn't get the start I needed to win the race and that was it."
Having won the test event, Reade appeared to be returning to the form she displayed in the run-up to Beijing, but injury problems affected her preparations in 2012 and she came to London very under-raced.
Reade tempted by track at Rio 2016
But the 6,000 noisy fans at the BMX track started to believe something special could happen for the 23-year-old from Crewe in the final.
Having won one of her three semi-final rides and recorded the second fastest time in the final run, Reade was given second choice of starting gates.
Australian Caroline Buchanan opted for a lane in the middle, giving Reade the inside line and a golden opportunity to show the devastating acceleration that helped her win world championship golds in the velodrome, and beat her seven rivals to the first corner.
It was not to be, however, as Reade arrived at the all-important hairpin in sixth and never threatened to improve that.
The 23-year-old now faces some difficult decisions about what she wants to do next, while Pajon can look forward to the adoration of a nation, the freedom of Medellin and whatever other honours Colombia can bestow.
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