Pol Espargaro set the fastest lap time during the first track session of the 2010 grand prix season - 125cc free practice, held at Qatar on Friday night.
The Tuenti Racing rider led team-mate Efren Vasquez by 0.312sec by the end of the one hour session for the only remaining two-stroke class, in which Derbi swept the top four places.
Third place went to Red Bull Ajo Motorsport rider Marc Marquez, who had knocked countryman Espargaro from the top with five minutes to go, with German Sandro Cortese the top non-Spaniard in fourth.
Reigning champion Julian Simon has moved to Moto2 for 2010 and his replacement, Nicolas Terol, claimed fifth place on his Aspar Aprilia debut.
Terol's team-mate and 2009 title runner-up Bradley Smith had a more troubled session, being left down in twelfth place and over 2.7sec off the pace after spending plenty of time in the pits in search of an effective set-up.
Fellow Briton Danny Webb displayed more speed, but fell from fifth place with 20mins to go and was unable to continue, dropping him to tenth by the flag.
Friday practice - Qatar:
1. Espargaro (Derbi) 2min 7.218s
2. Vazquez (Derbi) +0.312sec
3. Marquez (Derbi) +0.374sec
4. Cortese (Derbi) +0.952sec
5. Terol (Aprilia) +1.236sec
6. Krummenacher (Aprilia) +1.761sec
7. Zarco (Aprilia) +1.904sec
8. Rabat (Aprilia) +1.864sec
9. Koyama (Aprilia) +1.982sec
10. Webb (Aprilia) +2.043sec
12. Smith (Aprilia) +2.727sec