Andrea Dovizioso led an all-Ducati top four in first MotoGP practice for the Aragon Grand Prix, with Danilo Petrucci his nearest challenger by 0.190 seconds.
Pramac's Petrucci set the early pace in FP1 on his Ducati GP18 with a 1:50.254s, before Marc Marquez – who had Turn 10 renamed in his honour on Thursday – guided his factory RC213V to a 1:49.281s to take over from the Italian.
Marquez's Honda stablemate Cal Crutchlow cut the Spaniard's advantage down to just 0.008s moments later, though Marquez soon established a 0.4s gap with his follow-up la of 1:48.804s.
Misano race winner Dovizioso took over from Marquez with half the session gone by just 0.001s, which was matched by Maverick Vinales with six minutes remaining.
However, Dovizioso opened up an advantage on the timesheets of 0.7s with his first flying lap on a fresh hard rear with a 1:48.020s, which put the Italian just underneath the race lap record.
Petrucci slashed his Ducati stablemate's gap to just under two tenths with a 1:48.210s, while Pramac teammate Jack Miller put his year-old Desmosedici into third.
Jorge Lorenzo completed trailed the Australian by just under 0.020s to complete a Ducati 1-2-3-4 in FP1, with all of the top four setting their best laps on hard rubber.
Vinales was the first non-Ducati runner in the standings in fifth, a though some eight tenths off the pace, while Marquez was a further 0.001s adrift having elected against a late time attack.
Valentino Rossi was seventh on the sister works Yamaha, with Tech3's Johann Zarco a few hundredths adrift in eighth. Crutchlow and Suzuki's Andrea Iannone completed the top 10.
Dani Pedrosa made a low-key start to his Aragon weekend on the second Repsol Honda, the Spaniard – who was second in the Aragon race last year – almost two seconds off the pace in 18th.
While there were no crashes in FP1, Avintia's Xavier Simeon was forced to park up in the latter stages after the engine in his GP17 expired spectacularly on the run into Turn 1.
On the other side of the Avintia garage, former Moto2 race winner Jordi Torres made his MotoGP debut as he takes over from Christophe Ponsson as Tito Rabat's replacement for the weekend aboard Simeon's GP16s.
Torres, who last made a grand prix appearance at Aragon in 2014, brought up the rear of the 24-strong field with a 1:52.823s and 4.8s from Dovizioso's session-best time.
