Duarte held off the pack, to Ponzi's frustration
Britain's Ben Swift just missed out on a medal as Fabio Andres Duarte of Colombia won the under-23 men's race at the road cycling world championships.
Duarte broke away from a 10-man group with 1km left and just held on.
A frustrated Simone Ponzi of Italy finished second while German John Degenkolb was third, ahead of Swift.
"I knew I had to attack right then because, since I'm more of a climber, I knew I'd have no chance in a bunch sprint," said Duarte.
The lead group in the 173.35km race included three Italians but the hosts were unable to take advantage.
"I'm really happy to get the silver medal, but I'm feeling slightly bitter because I had pinpointed the final bend as a strategic point," said Ponzi.
"I did well to join the leaders ... and when the Colombian guy attacked I gave it everything to pull him back, but he was just too fast."
Swift, who rode well to reach the leaders in the final few laps, looked spent in the final few kilometres but hung on for his fourth spot. Last year's bronze medallist Johnny Bellis, came in 77th.
On Saturday, Britain's Nicole Cooke is one of the favourites in the elite women's road race.
And on Sunday, Italy's Paolo Bettini has the chance to win the elite men's road race for a third consecutive year.
His main rival for gold is Spain's Oscar Freire, who has won three previous titles.
The 15 laps on the undulating 17.3km (10.75 mile) course are even tougher than the one in Stuttgart, where Bettini won last year.
The terrain should dull Freire's sprinting powers while favouring Bettini's all-round strength.
"I am in better condition than last year. I know that I can win," said Bettini.
But Freire said: "Italy will try to ride a fast race to force a selection before the final lap.
"If we arrive at the finish in a group of 20 riders I think I have a good chance of winning."
David Millar, Steve Cummings and Geraint Thomas are the stars of the GB squad.
Men's under-23 road race results:
1. Fabio Andres Duarte Arevalo (Col) 4hrs 17mins 2secs
2 Simone Ponzi (Ita) at same time 3 John Degenkolb (Ger) at same time 4 Ben Swift (GB) at same time 5 Rui Costa (Por) at same time
Selected Others: 77 Jonathan Bellis (GB) 4hrs 22mins 25secs 88 Jonathan Mcevoy (GB) at 4:24'34
The role of a sprint cyclist