Tom Pidcock put in a gritty, determined performance in treacherous conditions to finish second in his first World Cup race of the season in Overijse.
The World Champion suffered an early setback as he had a bike issue as the race started, dropping to 31st overall, but a superb effort saw him carve through the field to make the front group of three by the second lap.
Pidcock was joined by Vanthourenhout and Eli Iserbyt, until the latter was distanced in the following lap.
Pidcock then gained a small advantage over Vanthourenhout as the laps progressed, both riders managing the technical course in terrible conditions.
The pivotal moment occurred on the penultimate lap as Pidcock suffered a small crash, allowing his Belgian rival to take the lead.
Pidcock trailed by 11 seconds at the start of the final lap and managed to reduce the gap to just three seconds, but Vanthourenhout held on to take a hard-fought victory.