Repsol Honda's Dani Pedrosa set the pace during the first MotoGP track session ever held at the Aragon circuit in Spain.
Pedrosa, now confirmed as staying at Honda for the next two years, will be seeking his fifth win of the season - and third in a row - on Sunday, and got his third home Spanish event of the season off to a strong start by finishing 0.411sec clear of the field.
Until the final seconds his advantage had been almost double that, but Ducati's Nicky Hayden suddenly launched up the order on his final lap of the 45-minute session, pushing world championship leader Jorge Lorenzo down to third for Fiat Yamaha.
Lorenzo's last lap then saw the seven time 2010 race winner get within 0.422sec of Pedrosa.
Fourth fastest was Hayden's team-mate Casey Stoner with Marco Simoncelli making an impressive start to be the top rookie and satellite rider, in fifth place for San Carlo Honda Gresini.
Simoncelli was just ahead of fellow Italian and reigning seven time MotoGP champion Valentino Rossi (+1.263sec from Pedrosa).
Aleix Espargaro christened the circuit with its first MotoGP crash after just three minutes when the Spaniard highsided from his Pramac Ducati.
Espargaro was unhurt and returned to the pits on the back of Fiat Yamaha team manager Wilco Zeelenberg's scooter - the Dutchman having been watching trackside at turn two.
That was only fall during the 45 minutes, although several riders unsurprisingly missed their braking points and took advantage of escape roads as they learned the circuit.
The fastest top speed was a 323.1km/h by Pedrosa. Honda and Ducati riders dominated the top half of the straight-line speed list, with the fastest Yamaha that of Tech 3's Colin Edwards who set a 315.9km/h for ninth.
In a change from the normal format, a second MotoGP practice session will be held this afternoon.
This weekend's practice and qualifying have all been reduced from one hour to 45 minutes to accommodate the extra Friday session.
Friday practice (1):
12. de Puniet