Repsol Honda's Dani Pedrosa ended day one of the Sepang MotoGP test on top of the timing charts on his RC213V.
The Spaniard's fastest lap in 2m 1.157s put him ahead of old sparring partner and reigning champion Jorge Lorenzo on the Yamaha M1, but only by 0.008s.
Pedrosa's team-mate and series rookie, Marc Marquez, was hugely impressive as he set the third fastest time in 2m 1.201s – 0.044s off the top spot.
Valentino Rossi was 0.427s behind Pedrosa on the factory Yamaha M1.
Pedrosa, last year's championship runner-up, said: “Basically it's the bike from Valencia. The difference from last year is the weight [3kg more for 2013] and today was more about trying to change the weight of the bike and it is working well.
“Also we did some tests regarding the longevity of the engine.
“I'm a little bit tired but it wasn't super hot today,” he added. “There are more things to try like shocks, suspension, something with the brakes.
“Today was more like a functional test,” he added.
"We've spent three months off the bike and the feeling from the first day testing is positive. Tomorrow we can go more into the suspension, the speed etc and other things.
“The track was quite good and it's been cloudy; here when it is too hot the grip is much less.”
On the performance of his new teammate and last year's Moto2 world champion Marquez, Pedrosa said: “He is going well, fast, though this is not a big surprise.”