Matija Frigan opened the scoring for the host in the 36th minute and Allahyar Sayyadmanesh made it 2-0 from the penalty spot in the 72nd minute.
Westerlo moved up to sixth place with 18 points, 10 points adrift of leader Genk.
It was the third goal of the Iranian winger in Westerlo.
The match was held at the Het Kuipje.