Nico Terol justified his status as pre-season championship favourite with a dominant display in the opening practice session in Qatar.
Last seasons title runner-up coped best with the windy conditions to set the fastest time at the Losail International Circuit.
The Bankia Aspar rider took the top spot just before the halfway mark in the 40 minute session, and stayed in front as the lap times dropped.
Terol set a time of 2:09.122 to leave him nearly a full second clear of nearest challenger Jonas Folger.
Luis Salom showed signs of carrying his late season momentum from 2010 into the new campaign as he claimed 4th ahead of the Avant-AirAsia-Ajo pair of Efren Vazquez and Johann Zarco.
Hector Faubel matched his Aspar teammate for most of the session but a flurry of late times saw him slip to 7th.
Miguel Oliveira was the top rookie after finishing in 9th place while his European 125cc rival Maverick Vinales also made a promising start in 14th.
Danny Kent was the best of the Brits in 12th place, while Danny Webb finished 16th for the new Mahindra Racing team.
Newcomers Harry Stafford and Taylor Mackenzie were 24th and 26th respectively.
With this weekend's action spread over four days, the lap times are sure to come down, with Free Practice 2 taking place at 17.55 GMT.