Nico Rosberg edged out Mercedes team-mate Lewis Hamilton to set the pace in the opening practice session ahead of the Italian GP at Monza.
The duo traded top spot throughout the first half of the session, but it was Rosberg who wound up fastest courtesy of an impressive 1:22.959, two tenths quicker than 2015 Monza winner Hamilton could manage.
Kimi Raikkonen was a second adrift of Rosberg's benchmark in third as home favourites Ferrari trialled an upgraded engine, with Sebastian Vettel fourth.
Force India looked strong once again as Sergio Perez took fifth, while Romain Grosjean was an encouraging P6 for Haas ahead of Valtteri Bottas.
Max Verstappen, who trialled the 'halo' cockpit protection device during the session, was eighth as Esteban Gutierrez and Daniel Ricciardo completed the top ten.
It was a solid, if uninspiring, start for McLaren, as Jenson Button, another to test the 'halo', and Fernando Alonso, who hit gearbox trouble late on, finished the session 11th and 13th, with Force India youngster Alfonso Celis, replacing Nico Hulkenberg, sandwiched between them.
Felipe Massa was 14th after being sidelined for much of the session with a turbo issue ahead of Sauber's Marcus Ericsson and Toro Rosso duo Carlos Sainz and Daniil Kvyat, braced for a difficult weekend with the 2015 Ferrari power unit.
Esteban Ocon took P18, out-pacing Felipe Nasr and team-mate Pascal Wehrlein in the Mercedes-powered Manor.
Renault's Jolyon Palmer and Kevin Magnussen propped up the order.