Lewis Hamilton set a searing pace in first practice at the Italian Grand Prix amid continuing fall-out from his clash with Nico Rosberg.
Hamilton beat McLaren's Jenson Button by 0.623 seconds, as Rosberg could manage only third, 0.808secs adrift of his Mercedes team-mate and title rival.
Ferrari's Fernando Alonso was fourth ahead of McLaren's Kevin Magnussen.
The track action came 24 hours after Mercedes F1 boss Toto Wolff warned his drivers to behave or risk being sacked.
The ultimatum came in the aftermath of the drivers' collision at the Belgian Grand Prix two weeks ago. A failed overtaking move by Rosberg led to the two colliding, effectively ending Hamilton's race while Rosberg went on to finish second and open a 29-point championship lead.
Wolff told BBC Sport on Thursday: "If we are not able to manage the two of them following the Mercedes-Benz spirit then we need to admit that."
Hamilton has arrived at Monza in a positive, almost buoyant mood, determined to close the gap to Rosberg after falling more than a win's worth of points behind for the third time this season.
Hamilton looked imperious on the track, comfortably clear of his rivals, although he was one of many drivers who had edgy moments, running wide as they came to terms with the tricky demands of heavy braking from more than 200mph for Monza's chicanes while running with the low-downforce set-up required at this high-speed track.
Alonso's fourth place is unlikely to reflect Ferrari's true competitive position at their home race - they have tended to look fast on Fridays this year only to fade back as the weekend goes on.
Red Bull's Sebastian Vettel was sixth fastest, ahead of the second Ferrari of Kimi Raikkonen.
But the Williams cars, which are expected to be Mercedes' closest challengers this weekend, had an understated session, Valtteri Bottas and Felipe Massa ending up 12th and 13th.
Williams tend to run their cars heavier on fuel on Fridays as they focus on the race, and then become more competitive on Saturday and Sunday.