Lewis Hamilton headed Valtteri Bottas to a Mercedes one-two in first practice at the Italian Grand Prix.
Hamilton was 0.435 seconds quicker than the Finn – and more than a second in front of title rival Sebastian Vettel, who is seven points ahead after 12 of 20 races.
The top eight was completed by Kimi Raikkonen in fourth followed by Red Bull’s Daniel Ricciardo and Max Verstappen and the Force Indias.
McLaren’s Stoffel Vandoorne was ninth.
Williams’ Felipe Massa was 10th while Vandoorne’s team-mate Fernando Alonso, running an upgraded Honda engine only in this session so it can be ready for Singapore in two weeks’ time, was only 15th.
Alonso is taking the grid penalty for the new engine – for using more than the permitted number of part – at this race because McLaren expect to be more competitive in twisty Singapore than at high-speed Monza.
The Red Bull drivers will also receive grid penalties for fitting too many engine parts.
Both will have new internal combustion engines, turbos and MGU-Hs, the hybrid part that recovers energy from the turbo.
The exact details of the penalty have not been officially confirmed, but it is likely Ricciardo will be penalised 25 places and Verstappen 15 because the Australian had used more parts before this race and so is hit differently by F1’s complex engine penalty system.
There was some light rain with just over 15 minutes to go at the famous royal park, but not enough to stop cars running, and there has been no sign so far of the heavy rain that was predicted for the entire day.
But the first signs were that Mercedes had a significant advantage over Ferrari.
The silver cars were quicker on the ‘soft’ tyres than Ferrari were on the ‘super-soft’ and Mercedes extended their advantage further when they fitted the quicker tyre.
Bottas was faster than Hamilton on the softs but the Briton reversed the positions on the super-softs.
However, Friday practice can be misleading and the qualifying and race-simulation runs in the second session will provide a clearer picture.
All leading drivers – and several others – had off-track moments at the first chicane and elsewhere as they explored the limits on this track where braking from high speed is a crucial part of a fast lap time.