Goal King Paul Onuachu was on course to grabbing the match winner before the new sensation in the Belgian league Union Saint-Gilloise held back Genk in stoppage time.
Onuachu scored his third goal of the new league season from the penalty spot in the 73rd minute.
However, visitors Union fought back to draw level five minutes into added time.
Last season, Onuachu netted 35 goals in all competitions for Genk.
Promoted Union are now second on the table with 13 points from seven matches, while Genk are fifth with 11 points.
