With speculation surrounding the German's future beyond 2012 continuing in the paddock, Schumacher came out firing with a one minute 25.422 second lap that no one could get within 0.3 seconds of.
Closest to him was Belgian GP winner Jenson Button (McLaren), who was sandwiched by the other Mercedes of Nico Rosberg in third position.
Fernando Alonso was fourth quickest, having stopped his Ferrari at the Variante Alta chicane with five minutes to go after suffering a suspected engine failure.
Alonso's team-mate Felipe Massa was fifth ahead of Lewis Hamilton in sixth, Kimi Raikkonen seventh. Sergio Perez, Mark Webber and Pastor Maldonado completed the top 10.
The Williams man also stopped out on the circuit just prior to the first Lesmo in the final moments.
China's Ma Qing Hua made history by becoming the first Chinese driver to take part in a race weekend as he drove in practice for HRT.
Ma did not shine on debut, however, finishing last and over five seconds off the pace, though he was within two seconds of team-mate Pedro de la Rosa by the end to complete a creditable first effort on what can be a daunting circuit with very low downforce.
After the usual exploratory tracks early in the session to assess grip levels, it was Schumacher that remained fastest for much of the morning in the rapid-down-the-straights Mercedes once the session swung into action properly.
First Massa, and then Raikkonen, posted early fliers before Hamilton emerged from the pits to set what was probably the first leaf-free lap on a track that cleaned up through the first half of the session.
Hamilton's time was a 1m26.346s, and the McLaren man set it just after the halfway mark.
It was not long after that Schumacher posted his best time, and that would stand for the rest of the 90 minutes.
A lap later though and he was bouncing over the bumps at the Variante Alta. He was not the only man to do so during the session, with Raikkonen, Sebastian Vettel, Webber, Massa and F1 rookie Ma among others to smash over the kerbs at the first and second chicanes.
World champion Vettel could not quite break into the top 10, just four thousandths slower than Maldonado, while Lotus sub Jerome D'Ambrosio was 15th, just over a second slower than Raikkonen.