Italian Grand Prix: Nico Rosberg heads Lewis Hamilton in practice
Nico Rosberg headed team-mate Lewis Hamilton as Mercedes dominated first practice at the Italian Grand Prix.
The German was 0.203 seconds quicker than Hamilton, with Ferrari's Kimi Raikkonen third, a second off the pace.
Mercedes set their times on the super-soft tyre, while Ferrari used the soft, which would account for about half the gap between the two cars.
Ferrari's Sebastian Vettel was fourth, ahead of Force India's Sergio Perez.
Hamilton enters the race nine points ahead of Rosberg in the championship after recovering from 21st on the grid to finish third at the Belgian Grand Prix last weekend, as Rosberg won.
Ferrari have used the last of their remaining engine development 'tokens' ahead of their home race in an attempt to boost their competitiveness after a slump in form that has seen them lose second place in the constructors' championship to Red Bull.
The fastest Red Bull was Max Verstappen in eighth, behind Haas driver Romain Grosjean and Williams' Valtteri Bottas, whose team-mate Felipe Massa announced on Thursday that he would retire at the end of the year.
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FIA concerns over Verstappen
Verstappen remains the focus of attention following his controversial battle with Raikkonen in Belgium.
Raikkonen has criticised Verstappen for being too dangerous, while the Dutchman said he would not change his driving because others were not happy.
The stewards took no action against Verstappen in Spa, but BBC Sport has learned that Charlie Whiting, the F1 director of governing body the FIA, felt that Verstappen's late move in defence at 200mph as Raikkonen attacked was on the edge of acceptability.
Whiting told the teams in a meeting on Thursday that he felt Verstappen could have received a black-and-white warning flag for his driving.
The black-and-white flag is an indication of unsportsmanlike behaviour and is only shown once. If the driver commits the same offence again he can be disqualified from the race.
Whiting's intervention raised the stakes in the debate ahead of the drivers' briefing after practice on Friday afternoon, where the incident is expected to be discussed.
It was a relatively low-key session on track, despite a number of drivers running off the track at the tricky Monza chicanes in the warm sunshine.
McLaren's session came to an unfortunate end as Fernando Alonso was forced to pit with a gearshift problem. He was 13th, with team-mate Jenson Button 11th, the drivers expecting their most difficult weekend of the year because of the lack of power of the Honda engine, which still lags despite recent updates.
Button and Verstappen ran the halo head protection system in the first part of the session as trials continue ahead of the planned introduction of the device in 2018.