Belgian Remco Evenepoel added the Olympic gold to his world title on Saturday, defying rain and a strong field to win the 32.4km individual time trial in Paris.
The 24-year-old was almost 15 seconds faster than Italian Filippo Ganna in second while another Belgian, Wout van Aert, took bronze at 25sec.
British hope Josh Tarling finished fourth two seconds behind after losing time on an early puncture.
A day after it rained on the opening ceremony, dark skies hung low again over Paris as the first cycling event embarked from the military museum at Invalides.
At the ramps where riders set off at one-minute intervals Tarling and Ganna were pre-race favourites.
Evenepoel set off at a lightning pace and was in the lead at every time check.
Ganna saved his fastest form for the finale, a five-kilometre home straight and in the final section overhauled Van Aert to move from third to second.
Evenepoel, a much smaller man, did better on his cornering than the other two medallists who are much larger men.
On the streets through the French capital he chose his line better and accelerated out of it sooner.
Evenepoel came third overall in the Tour de France last weekend, won the white jersey as best young rider and also won one of the time trials.
The Belgian was world time trial champion in 2023 and world road race champion in 2022 and will target an Olympic double next weekend in the 273km road race.
