Casey Stoner has been sidelined by a pulled back muscle as MotoGP teams unveiled their new 1000cc bikes on the first day of pre-season test runs.
Spaniard Jorge Lorenzo shook off any rust from missing the final three races of 2011 due to injury by posting the fastest time.
Yamaha dominated to open the three days of tests at Sepang in Malaysia, with three of its riders among the top four.
The testing session marked an emotional return for riders to the Sepang circuit for the first time since Honda rider Marco Simoncelli died there in a shocking crash in October’s Malaysian MotoGP.
On Monday, Honda team officials laid a flower wreath at turn 11, where the 24-year-old Simoncelli was killed, and observed a moment of silence.
Lorenzo’s 2011 season ended prematurely when he crashed during warm-ups for the Australian Grand Prix.
But he set the fastest pace on Tuesday on his Yamaha in hot and humid conditions with 2.0 min 01.657 seconds while his countryman Dani Pedrosa with rivals Honda was next with a time of 2:02.003.
Yamaha’s Carl Crutchlow of Britain posted a third-best 2:02.221 while his teammate Ben Spies of the United States followed up in 2:02.234.
MotoGP has moved to 1000cc bikes this year in place of the earlier 800cc engines.
Stoner failed to show whether he could maintain his form on the new bikes after pulling a back muscle while stretching just before morning testing, keeping him off the track.
Pedrosa shrugged off the strong Yamaha performance, saying he was still getting the feel for his new Honda.
“I am focused on myself. I was most of the time alone on the track and was not mixing with the other MotoGP riders.
“I hope to do better tomorrow. Tomorrow we will start (to find) the proper setting of the bike,” he said.
Test runs were delayed in the morning after rain left the track damp.
Multiple world champ Valentino Rossi, who struggled through a difficult 2011 season, posted a fifth-fastest lap time of 2:02.392 astride his Ducati Desmosedici GP12.
Testing ends on Thursday and is followed by another three-day session at Sepang beginning February 28.
The MotoGP 2012 season will officially start on April 8 in Qatar.
