The result moved fourth-placed Belgium to within two points of the third-spotted Turks ahead of Wednesday's final round of matches.
It was a lively and exciting match in the Belgian capital, with action switching from end to end rapidly although Belgium looked the more likely going forward.
Belgium goalkeeper Logan Bailly was forced to punch away Ceyhun Eris' early blast for a corner in the fourth minute as Turkey pushed for an early opener.
But four minutes later the first goal arrived at the other end through striker Mpenza. He was sent clear by Roland Lamad from the right side for a free run into the penalty area, and finished the move off with a shot which gave Turkey goalkeeper Volkan Demirel no chance.
Volkan had to be alert two minutes later to prevent Belgium going two goals clear, saving a shot from Kevin Mirallas from inside the penalty area.
Mpenza was denied a second in the 27th minute when he found himself through one on one but the Turkey keeper made the save.
Bailly again used his fists to keep out a Nihat Kahveci header just after the half-hour mark in a rare Turkey attack.
Five minutes into the second half, Lamad saw his long-distance effort caught by Volkan and the keeper then also kept out a 12-yard effort from Daniel van Buyten after he had been set free by Moussa Dembele.
Substitute Eden Hazard forced a brilliant save from Volkan nine minutes from time, diverting his fierce attempt away from the bottom-right corner.
However, the second Belgium goal arrived two minutes later when Hazard fed Mpenza. He had another free run on Volkan and this time gave the keeper no chance.