Tau started his first league encounter this season, as his side looked to edge closer to the top of the table with Zambian Fashion Sakala given a run by the hosts.
Oostende didn't wait long to go ahead after Hendrik Van Crombrugge struggled to hold onto Makhtar Gueye's fiercing shot on 11 minutes, allowing Robbie D'Haese an easy tap-in.
The away side could've levelled seven minutes thereafter, but Jeremy Doku could unfortunately not get the better of Oostende goalkeeper Guillaume Hubert.
Anderlecht fell further behind four minutes following the half-hour mark after Gueye tucked home from the penalty spot following a foul in the area.
Kompany's boys halved the deficit soon after through Adrien Trebel, who drilled in an absolute blinder of a strike that gave the opposite number no chance.
Another offensive change by Kompany at halftime had Lukas Nmecha setting in for Antoine Colassin in a quest to turn the game around.
Trebel would then provide an assist for Tau, who netted the equaliser on 54 minutes with a well-taken finish after Oostende went to sleep at the back for his second goal in three matches.
Tau went in search of another soon following the remaining minutes, however was met by a resilient Hubert who managed every threat coming their way.
Oostende tried to regain the lead before fulltime, but Anderlecht tracked back to pick up a point on the road and remain unbeaten while KV Oostende are still winless near the foot of the table.