Bradley Smith set the pace by almost one-second during a wet, windy and delayed 125cc free practice session at Phillip Island in Australia on Friday.
The Aspar Aprilia rider took first place from title leader Marc Marquez with one minute to go, then pushed his advantage up to 0.925sec on his 20th and final lap.
Marquez regained the 125cc championship advantage with his eighth victory of the season last time out in Malaysia, in very different conditions.
But the challenging weather did help 16-year-old Danny Kent show his talent.
The young Briton, riding in only his fourth grand prix, setting the third fastest lap time for Lambretta, less than two tenths from the Ajo Derbi of Marquez.
Nico Terol, who starts round 14 three points behind title leader Marc Marquez, was fifth fastest with Pol Espargaro, the third and final of the 2010 title contenders, seventh for Tuenti Derbi.
Friday practice – Phillip Island:
1. Smith (Aprilia) 1m 54.547s
2. Marquez (Derbi) +0.925s
3. Kent (Lambretta) +1.108s
4. Cortese (Derbi) +1.136s
5. Terol (Aprilia) +1.373s
6. Zarco (Aprilia) +2.201s
7. Espargaro (Derbi) +2.626s
8. Koyama (Aprilia) +3.049s
9. Krummenacher (Aprilia) +3.051s
10. Grotzkyj (Aprilia) +3.091s
13. Webb (Aprilia) +3.542s