The 22-year-old crashed on the third stage of the race after losing control of his bike and colliding with a concrete bridge over a ditch. He died as a result of his injuries.
The cycling world was led at the funeral by Lambrecht's Lotto-Soudal teammates and team manager Marc Sergeant. German sprinter Andre Greipel was also present.
A giant screen on the wall of the church showed black and white photos of Lambrecht and a Lotto cycling jersey was placed on the coffin.
Lambrecht was one of Belgium's great cycling hopes. He won the Under 23 Liege-Bastogne-Liege and finished second in the Tour de l'Avenir in 2017 behind this year's Tour de France winner Egan Bernal before turning professional last year with Lotto-Soudal.
This year he placed 12th at the Criterium du Dauphine, winning the best young rider category, fourth in La Fleche Wallonne and sixth at the Amstel Gold Race.