From the early exchanges it was clear that Montreal were keen to deliver crosses on a regular basis, and the Chicago defence were sent a warning when Drogba's header was kept out by Jon Busch.
A fifth goal in as many MLS games from Drogba handed the hosts the control, but Chicago recovered well to earn spells on top either side of the break.
Chicago needed less than five second-half minutes to get back on level terms as Gilberto hit the post with a header, before David Accam reacted quickest to nod in the rebound.
The visitors then started to look the sharper of the two sides, but they missed a great chance to take the lead when Accam created space by evading a couple of challenges in the box before wasting the opportunity by chipping his shot over the crossbar.
Montreal capitalised on the miss just a few moments later when Romero collected a pass from Patrice Bernier before curling home to score what proved to be the winning goal.
It was a nervy finish for Montreal when they lost Laurent Ciman to a second yellow card late on, but the hosts survived as Bush kept out a Larentowicz header in stoppage time to clinch the points.