Jorge Lorenzo beats Dani Pedrosa to Qatar win.
Australian Stoner - who dominated the championship last season - then opened up a near two-second lead and looked likely to win in Qatar for the fifth time in the last six years.
But with five laps remaining Stoner's pace began to drop as he struggled with arm pump - when the huge braking forces required to stop from 210mph cause muscle spasms in a rider's forearm - and Lorenzo and Pedrosa were both able to pass the champion.
results:
1. Jorge Lorenzo (SPA) Yamaha 42:44.124
2. Dani Pedrosa (SPA) Repsol Honda 42:45.066
3. Casey Stoner (AUS) Repsol Honda 42:47.122
4. Cal Crutchlow (GBR) Tech 3 Yamaha 43:01.328
5. Andrea Dovizioso (ITA) Tech 3 Yamaha 43:01.634
6. Nicky Hayden (USA) Ducati 43:12.627
7. Alvaro Bautista (SPA) Gresini Honda 43:12.660
8. Stefan Bradl (GER) LCR Honda 43:13.678
9. Hector Barbera (SPA) Pramac Ducati 43:15.598
10. Valentino Rossi (ITA) Ducati 43:17.879