A typically competitive opening Monaco session involved the top spot being exchanged repeatedly in the final minutes as the track conditions improved, and in the end it was Sebastian Vettel who emerged in front for Red Bull ahead of Ferrari's Fernando Alonso.
Schumacher crashed in practice © LAT
But while one Red Bull led the way, the other propped up the order - a gearbox problem meant Mark Webber did not get to set a time at all.
Nico Rosberg was third for Mercedes, followed by Felipe Massa's Ferrari and the two McLarens. The sister Mercedes of Michael Schumacher took 10th despite the former champion slewing into the Sainte Devote barriers after making a late decision to drive up the escape road.