Red Bull pair Sebastian Vettel and Mark Webber set the fastest two times in Friday's first practice for the Chinese Grand Prix, well ahead of their Formula One rivals.
Vettel was six-tenths of a second faster than Webber around the Shanghai International Circuit, with a gap of a further 1.5 seconds back to the McLaren pair of Lewis Hamilton and Jenson Button.
Renault's Nick Heidfeld set the fifth-best time before spinning and crashing into a wall, while Ferrari's Felipe Massa was sixth on the timesheets.
Sauber's Sergio Perez, Williams' Pastor Maldonado, Renault's Vitaly Petrov and Sebastien Buemi of Toro Rosso rounded out the top 10.
On an unseasonably warm day, with the track shrouded in smog, most teams chose to drive an unusually high number of laps as they attempt to gain more understanding of the new Pirelli tires. Webber did the most of any driver, with his 27 laps representing almost half Sunday's race distance.
Ferrari's Fernando Alonso was a contrast, only emerging late in the session when more rubber had been laid on the track, and was 12th fastest.
It was another sobering session for Mercedes, whose car performed well below expectation in the opening two races in Australia and Malaysia. Nico Rosberg was 11th fastest, with Michael Schumacher all the way down in 18th, behind the likes of Toro Rosso reserve driver Daniel Riccardo, and Lotus' Heikki Kovalainen.
A number of drivers ran off the circuit, which is a challenging one for engineers, who must balance the low downforce needed on the very long straight against the high downforce required for some very tight, long corners.
Heidfeld had the most noticeable incident, spinning after he went over a curb and sliding across the track into a wall, snapping the front wing off the Lotus.
A second practice session was scheduled for later Friday, and a third session on Saturday before qualifying.
