كتب : وكالات
Italian defender Mattia Notari was sent off on 30 minutes for a second bookable offense, paving the way for Westerlo to ease past the visitors.
Midfielder Rachid Farssi opened the scoring just one minute later and Daniel Chavez wrapped up the victory with a 54th-minute strike.
Lierse had to do without Egyptian attacking midfielder Mohamed Abdul-Wahed, who is nursing an ankle injury.
His compatriot Mohamed Al-Gabbas started on the bench before being introduced seven minutes past the hour mark.
The dismal start of Lierse, who are owned by Egyptian businessman Maged Samir, leaves them second from bottom in the league table with one point from seven matches.