Jorge Lorenzo marked his return to the track after last year's injury with the fastest time in the first pre-season MotoGP test at Sepang, while reigning champion Casey Stoner sat out the session with back pain.
Stoner aggravated an old back injury while warming up before going out this morning. After receiving physio, he decided to wait until tomorrow before taking to the track, with Honda test rider Kousuke Akiyoshi doing a handful of laps on his bike instead.
At the front, Yamaha rider Lorenzo set the pace with a lap of 2m01.657s, 0.2 seconds slower than last year's pole time at the Malaysian Grand Prix venue, and 0.346s ahead of second-placed Dani Pedrosa's Honda. 2010 champion Lorenzo was making his first appearance for Yamaha since his '11 campaign was ended prematurely by a serious hand injury sustained at Philip Island.
Yamaha had three bikes in the top four, with Tech 3 rider Cal Crutchlow impressing in third place and Ben Spies putting the second factory bike fourth. Crutchlow's new team-mate Andrea Dovizioso was sixth as he got back up to speed after breaking his collarbone in a recent motocross accident.
Valentino Rossi took an encouraging fifth on the best of the Ducatis, 1.1s off the pace, and 0.8s quicker than team-mate Nicky Hayden - another man recovering from a winter injury.
A handful of the new CRT bikes were present, but a long way off the pace, with Forward Racing's Colin Edwards 6.6s down on Lorenzo on his Suter-BMW, although he did lose mileage to electrical problems. The Avintia FTR-Kawasakis of Jordi Torres and Ivan Silva were several seconds slower still.
Fellow CRT squads Aspar and Speed Master had already begun testing in a private session at Valencia on Monday, where Aspar's Randy de Puniet was quickest on 1m35.3s - 3.5s slower than the 2011 MotoGP pole time.