Roberts totalled 155.2 points in the two combined sections to beat Japanese favourite Sorato Anraku into second place.
The 19-year-old was third after the boulder round at Le Bourget Climbing Venue but produced a brilliant lead climb for 92.1 points, and his gold was sealed when Anraku fell just under 10 points from Roberts’ mark.
Austria’s orld champion Jakob Schubert took bronze and Britain’s Hamish McArthur finished fifth on 125.9 points.
The teenage gold medallist was previously given the nickname ‘The Terminator’ because of his determination, having taken up the sport as an after-school activity.
A jubilant Roberts said: “I’m just absolutely lost for words. To find out that I got the gold in that moment, it was just truly incredible.
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