Zambian striker and former Wadi Degla and Nkana danger man Ronald Kampamba also known as Satesate was introduced for the first time in his new club as a substitute in the 83rd minute replacing Ibrahim Sabaouni.
His introduction however did not help Lierse who went on to concede a goal aminute later and Union’s third of the night.
The match was played at the Stade Joseph Marien in Brussels.
Union scored a first half goal through Vincent van Diepenbeeck for a first half 1-0 lead before Nicolus Rajsel extended the lead in the 82nd minute.Augusto D a Silva completed the rout 2 minutes later.
The loss condemns Lierse to the relegation zone at position 10 having played 22 matches with 31 points.
League leaders Antwerp’s stay at the top was not tempered with after second placed Tubize also lost 2-1 away at Virton.
Lierse is the home of Kenyan International Ayub Masika who did not feature in the match.