Felipe Massa picked up where he left off after his victory in the European Grand Prix at Valencia as the Ferrari driver set the pace on the first day of testing at Monza.
The Brazilian began work developing the Scuderia's aero package for the Italian Grand Prix, concentrating on set-up.
Massa completed three long runs, which he declared himself satisfied with - ending the day with a lap time of 1:23.428.
McLaren's Heikki Kovalainen, in low-downforce trim, was just over a hundredth slower, as was the Williams of Nico Rosberg - boding well for a competitive race at Monza next month.
Sebastian Vettel continued his and Scuderia Toro Rosso's impressive form with the fourth fastest time of the day ahead of Rubens Barrichello's improving Honda in fifth.
Mark Webber was sixth fastest for Red Bull.
Nick Heidfeld embarked on the first of two days at the wheel of his BMW F1.08, testing mechanical set-ups for Spa and Monza as well as suspension, aero and gearbox ratios.
Vitantanio Liuzzi returned to the cockpit of the Force India car, completing 99 laps and lapping less than second off Massa's pace to go eighth.
Jarno Trulli was ninth for Toyota while Nelson Piquet completed the runners in tenth.
Pos Driver Team Time Laps
1. Massa Ferrari (B) 1:23.428 101
2. Kovalainen McLaren-Mercedes (B) 1:23.439 78
3. Rosberg Williams-Toyota (B) 1:23.461 60
4. Vettel Toro Rosso-Ferrari (B) 1:23.691 99
5. Barrichello Honda (B) 1:23.827 85
6. Webber Red Bull-Renault (B) 1:24.005 96
7. Heidfeld BMW Sauber (B) 1:24.075 77
8. Liuzzi Force India-Ferrari (B) 1:24.239 99
9. Trulli Toyota (B) 1:24.510 92
10. Piquet Renault (B) 1:24.546 117