Van der Poel rode clear in opening minute of the race to defend rainbow jersey, Pidcock took second, Aerts third.
Frozen temperatures, heavy rain, and an extremely difficult course combine to make Namur World Cup race one of crashes, abandons, and epic racing.
20-year-old multi-discipline star forgoes a shot at the WorldTour in 2020 in favor of challenging for 'cross worlds while also racing road, gravel and mountain bike.
Van der Poel took third European title while Kastelijn dominated the race to take her first championship win on a boggy course in Italy.
The third round of the Cyclocross World Cup series saw Iserbyt extend his series lead with a third win, and Worst go solo from the start to take victory.
Iserbyt wins U23 worlds after Toupalik celebrates early
Eli Iserbyt and Laurens Sweeck, both Belgian, will toe the line in Tabor as outright favorites in the junior and U-23 races, respectively