A fully-focused Nico Rosberg topped the times ahead of his Mercedes team-mate and championship leader Lewis Hamilton in Friday's opening free practice for this weekend's Italian Grand Prix.
The 31-year-old German, who trails the defending three-time champion by nine points in the title race, clocked a best time of one minute and 22.959 seconds in warm late-summer sunshine at the high-speed Autodromo Nazionale.
Briton Hamilton was 0.203 seconds adrift of his team-mate as they began preparations for a race in which he hopes to complete a hat-trick of Italian triumphs and register his 50th Formula One victory.
Finn Kimi Raikkonen was third in the leading Ferrari ahead of his team-mate, four-time champion Sebastian Vettel, but the two scarlet cars were more than a second off the leaders' pace.
Mexican Sergio Perez was fifth quickest for Force India ahead of Frenchman Romain Grosjean of Haas, Finn Valtteri Bottas of Williams and the under-scrutiny Dutch teenager Max Verstappen in his Red Bull.
The 18-year-old driver had earlier been involved in a meeting with the International Motoring Federation (FIA) Race Director Charlie Whiting, together with Red Bull team manager Jonathan Wheatley.
This followed his aggressive racing during last weekend's Belgian Grand Prix after which he was criticised by both Ferrari drivers, and others, and it was discussed at Thursday's team managers' meeting at Monza.
Another Mexican Esteban Gutierrez of Haas and Australian Daniel Ricciardo in the second Red Bull completed the top ten as temperatures rose in the closing stages.
The air temperature was 27 degrees Celsius and the track 35, conditions that are sure to test the durability of the tyres in Sunday's race.
Ferrari may have been buoyed by their early showing as it was the first time the team ran its latest updated power-unit, having used up all of its permitted final development tokens for its home event.
Customer team Haas also took the 'new spec' engines and responded with sixth and ninth places.
Ferrari's 'spend' of three tokens for Monza means the team has used all 32 tokens for the season.
Rival engine suppliers Honda, Mercedes and Renault all have tokens to spare for the final seven races with two-time champion Fernando Alonso forecasting that his McLaren Honda team will gain performance in the final fly-away' part of the season.
"Despite recent progress, we are still struggling here a lot," he said. "But, from Singapore onwards, we will enjoy the races because our car is capable to be in the points every race and both cars in Q3.
"Here, being in the points would be completely unexpected."