Lewis Hamilton led Nico Rosberg in a Mercedes one-two ahead of both Red Bulls in first practice at the Japanese Grand Prix.
Hamilton was 0.330 seconds quicker than Rosberg, who was 0.281secs clear of Sebastian Vettel, with Mark Webber just 0.019secs off his team-mate.
The Ferraris of Felipe Massa and Fernando Alonso were fifth and sixth, just under a second off the pace.
Lotus's Romain Grosjean and Kimi Raikkonen were seventh and eighth.
McLaren's Sergio Perez took ninth, with Toro Rosso's Daniel Ricciardo breaking up the two-by-two formation in 10th, ahead of the Mexican's team-mate Jenson Button and Sauber's Nico Hulkenberg.
It was an incident-packed session. Two rookie drivers crashed at the notorious Degner Two corner, while Williams's Pastor Maldonado spun off at Spoon when he lost his left rear wheel.
Marussia's Jules Bianchi and Caterham's Giedo van der Garde had different incidents at the second of two tricky right-handers at Degner.
Bianchi crashed at the exit, and said he got his sleeve caught between the seat and the chassis and could not wind off the opposite lock he had applied to correct a slide.
The Frenchman will miss Friday's second session because of chassis damage sustained in his crash. The team say there is not enough time to repair the car. He will be able to drive in final practice on Saturday.
Van der Garde got on to the kerbs on the entry and slid off before getting to the corner. He questioned over the radio whether something had gone wrong with the steering.
He later accepted it was his own mistake, tweeting: "I was testing [a] different downforce configuration, [the crash] clearly showed us it was not optimum!"
Both Grosjean and Alonso ran wide and into the run-off area at the double left-hander called Spoon Curve on their first flying laps, the Ferrari driver straight after running wide at the hairpin.
The mistakes left Alonso 0.139secs slower than Massa. The Spaniard improved a couple of laps later to be just 0.028secs off the Brazilian.
"You have to respect the first session," said BBC F1 technical analyst Gary Anderson, "the track is dirty and it's very tricky if you get off line. It's not a session to go out and make mistakes."
The second session starts at 06:00 BST, and will see drivers simulate a low-fuel qualifying run and then do race-simulations on heavy fuel loads.