Florence - Alberto Rui Costa stunned Spanish rival Joaquin Rodriguez at the finish line of the world championships' road race to become the first Portuguese winner of the coveted rainbow jersey on Sunday.
Rodriguez finished second to take the silver with compatriot Alejandro Valverde taking bronze at the end of rain-hit 272.2km epic that claimed several pre-race favourites as well as the entire British team.
Italy's Vincenzo Nibali had to settle for fourth after being left with no teammates for the thrilling finale in the final stages of the 10th and last lap of a hilly 16.9km circuit around Florence.
Rui Costa, who won two stages at July's Tour de France as well as the Tour of Switzerland, succeeds Philippe Gilbert of Belgium as world champion.
Gilbert's Belgian team looked among the strongest amid a reduced, 42-man field on the final lap.
However the defending champion, as well as pre-race favourite Fabian Cancellara of Switzerland, were among those unable to respond when Rodriguez countered an attack by Nibali late on the second of the circuit's three climbs.