* Hamilton fastest in both Friday practice sessions
* Mercedes looking faster than ever
* Vettel third quickest for Ferrari (Adds quotes, grid penalties)
By Alan Baldwin
MONZA, Italy, Sept 4 (Reuters) - Formula One world champion Lewis Hamilton set the pace in practice for the Italian Grand Prix on Friday with dominant Mercedes turning on the power and leaving their rivals trailing.
The Briton, who will be chasing his 11th pole position in 12 races on Saturday, told reporters on arriving at Monza with his hair dyed blond that he was going through an 'experimental' phase.
There was nothing radically different in his track performance, however, only clear evidence that the upgraded Mercedes power unit was faster than ever.
The championship leader, 28 points clear of closest rival and team mate Nico Rosberg with eight races remaining, lapped nearly half a second faster than the German in sunny morning conditions.
The Briton, winner of six races so far this season, was however only 0.021 quicker than Rosberg in the afternoon, when he produced his fastest lap of one minute 24.279 seconds on the quickest track on the calendar.
"Today was a good day," said Hamilton. "I had a bit of a break in the second session but it was just so the team could check a few spikes in the data and everything was OK in the end.
"I didn't particularly hook up the first two sectors this afternoon, they were definitely better in the morning," he added. "So I'm sure there's some pace to find and I'll be looking through the data tonight to find it."
Ferrari's Sebastian Vettel, preparing for his first Italian race in the home team's red overalls, was third quickest in both sessions -- a massive 1.588 slower than Hamilton in the morning and 0.759 adrift after lunch.
That will have come as a disappointment for the fervent local fans, displaying the usual array of Ferrari banners in the stands including several supporting stricken favourite Michael Schumacher and the late Jules Bianchi.
"The first two cars are quite far away unfortunately, maybe we can get a bit closer tomorrow and we'll see what happens in the race," said Vettel.
Mercedes-powered Force India were fourth in both sessions, with Nico Hulkenberg in the morning and Sergio Perez in the afternoon.
The opening session was halted briefly when Spaniard Carlos Sainz lost control of his Toro Rosso at Parabolica and skidded into the gravel, bringing out the red flags at the half hour mark.
Honda-powered McLaren, stacking up more grid penalties for engine changes to both Fernando Alonso and Jenson Button's cars, endured difficult sessions with the Briton 18th and 19th respectively.
There were no problems with the Pirelli tyres after alarming high-speed blowouts in Belgium two weeks ago.
Five drivers collected grid penalties due to unscheduled engine and gearbox changes with Red Bull's Australian Daniel Ricciardo leading the list with a 25 place drop.
Russian team mate Daniil Kvyat will fall 15 places, with Red Bull sacrificing Monza to ensure they have fresh power units for the next race in Singapore, a slower circuit which should be much more suited to their car.
Sainz and Alonso each collected 10 place drops and Button loses five on Sunday's grid. (Reporting by Alan Baldwin; Editing by Justin Palmer and Ken Ferris)