Pidcock was a picture of composure during the taxing event, leading throughout the second half of the 28.25km race to finish 20 seconds ahead of nearest rival Mathias Flueckiger.

"Once we started I was fine, all the nerves kind of went and I concentrated on the race," the 21-year-old said.

"I'm happy this s**t (the Olympics) is only every four years because it's f***ing stressful.

"It's nothing like any other race."

Pidcock is the first Brit to claim a mountain-biking Olympic medal, while he bettered Jenny Rissveds' win in Rio at age 22 to become the youngest Olympian to win the men's or women's race.

It came less than two months after the Yorkshireman suffered a broken collarbone after being hit by a car while training.

"It's been a such a hard time, coming here from crashing," Pidcock said.

"That's just unbelievable.

"I know that my mum and girlfriend are crying at home. It's sad that they can't be here but I see them when I get home."

Spaniard David Valero Serrano finished strongly to snatch bronze, consigning Rio 2016 champion Nino Schurter to fourth place.

A misstep from Flueckiger, who momentarily got off his bike while navigating a climb, helped Pidcock enhance his lead over the Swiss silver medallist to 11 seconds after the fifth of seven laps.

Pidcock never looked back on the challenging 4.1km course, avoiding the sort of drama that resulted in Dutchman Mathieu van der Poel and Czech Ondrej Cink failing to finish.

The opening minute of the race was marred by gold-medal contender van der Poel's crash.

Van der Poel, who like Pidcock is a multi-discipline marvel, was competing after wearing the leader's yellow jersey for six days during an impressive Tour de France debut this year.

The 26-year-old went over the handlebars while attacking Sakura Drop, a tricky section the race guide ominously predicted would have riders "hurtling out from atop a ridge as if they were cherry blossom petals soaring over Mount Fuji".

Van der Poel got back on the bike before pulling out of the race during his fifth lap.

Australian Dan McConnell, whose wife Bec looms as a medal contender at the same venue on Tuesday, finished 30th after having issues with his bike and gears.

"It's disappointing," Dan McConnell said.

"I just couldn't put full laps together."

Bec McConnell has collected bronze at the past two world championships.

"Tomorrow's going to be a big day," husband and coach Dan said.

"It never is super-easy to watch her - it's quite stressful.

"But ... we're fairly used to it now."

Australian Associated Press