Tom Pidcock was unable to retain his UCI Mountain Bike World Championships title, taking bronze as South African Alan Hatherly powered to a first rainbow jersey in Andorra.
Hatherly, who took bronze in the Paris Olympics behind Pidcock and Frenchman Victor Koretzky, also stood on the third step of the podium in Friday's short-track race.
But he upgraded those third places with a composed, tactically brilliant ride in the Olympic cross-country, leading from the fourth lap and proving too strong for his rivals in the closing stage of the race.
He launched an uncharacteristically early attack towards the beginning of the fourth lap and the move paid off.
Koretzky had ridden toe-to-toe with the South African throughout the course but could not fight back onto his wheel after Hatherly attacked again, this time over the top of the steepest of several climbs on the final lap.
Koretzky finished 22 seconds behind the South African, who had time to celebrate the biggest win of his career as he approached the line, with Pidcock 39 seconds back on the winner.
The Frenchman would have been the first man in history to win the golden double of both the short-track and cross-country World Championships in the same year, having won the shorter race on Friday. He had to settle for the silver medal to match his Olympic gong of the same colour.
Paris champion Pidcock looked fatigued throughout the brutal up-and-down course in Pal Arinsal and despite a surge in the final lap to overtake compatriot Charlie Aldridge, he did not have the legs to bridge across to the leading duo of Hatherly and Koretzky.
Aldridge added a hard-fought fourth place to his silver medal in the short-track race and led the field on the third lap, leaping into the lead on a technical section, before fading.
Pidcock set off from the first row but quickly slipped to 21st position and expended valuable energy maneuvring his way through the bunch.
He fought well to almost get within reach of Koretzky and Hatherly at the start of the final lap, but the sight of the Olympic champion approaching appeared to spur the leading duo to dig deep once more.
Pidcock was immediately distanced again and could not drag himself back into contention for gold, while Koretzky too suffered from his late acceleration and could not follow Hatherly's counterattack.
The World Championships programme had to be altered for the final day of competition due to a heavy thunderstorm forecast to hit Andorra on Sunday afternoon. All of the races were shortened and brought forward in the day, with the men racing six laps of the hilly, high-altitude course, rather than the planned seven, and the women five rather than six.
Following the rescheduling the women's elite and under-23 Olympic cross-country races were held at the same time. The Netherlands' Puck Pieterse led the elite field for much of the day and took a well-deserved rainbow jersey, with compatriot Anne Terpstra second, 59 seconds back.
Italy's Martina Berta rounded out the podium. Great Britain's Evie Richards finished sixth, 1:51 down on the winner, having struggled to regain her position following an early crash.
French veteran and Olympic champion Pauline Ferrand-Prévot was another alongside Pidcock to possibly suffer post-Paris fatigue as she finished 14th in the final mountain bike race of her career.
