World champion Marc Marquez recorded the fastest time on day one of the 2014 season's first test session in Sepang.
The Repsol Honda rider finished ahead of Yamaha's Valentino Rossi, with Marquez's team-mate Dani Pedrosa third.
Great Britain's Bradley Smith was 10th, with Cal Crutchlow in 14th after the first session of the three-day event.
Marquez, 20, became the youngest MotoGP champion at the season-ending Valencia Grand Prix in November, winning the world title in his rookie year.
The Spaniard clocked two minutes 0.286 seconds in Sepang to finish half a second ahead of six-time MotoGP champion Rossi.
Both the Italian and Pedrosa moved ahead of Yamaha's Jorge Lorenzo, who lost his world crown to Marquez last year, in the final minutes of the day.
Track temperatures dropped in the last hour of the day in Malaysia, helping riders record quicker times.
Official Test Sepang - Session 1
1. Marc Marquez (Spa) Repsol Honda 2:00.286
2. Valentino Rossi (Ita) Yamaha +0.518
3. Dani Pedrosa (Spa) Repsol Honda +0.620
4. Jorge Lorenzo (Spa) Yamaha +0.796
5. Alvaro Bautista (Spa) Honda Gresini +0.954
6. Stefan Bradl (Ger) LCR Honda +1.034
7. Aleix Espargaro (Spa) NGM Mobile Forward Racing +1.133
8. Andrea Iannone (Ita) Pramac Ducati +1.252
9. Pol Espargaro (Spa) Tech 3 Yamaha +1.348
10. Bradley Smith (GB) Tech 3 Yamaha +1.590