Alex Rins claimed his maiden Moto3 victory at Austin in a race split by a severe accident for Jasper Iwema.
The Dutchman suffered a horrible high-side on lap 12, and had to be treated on the track after landing on his neck.
The medical team later reported that his vital signs were OK, while Iwema was conscious enough to move his arm while on the stretcher.
His crash led to a final five-lap shootout, with the order reset to the lap 10 standings - the final full lap completed before the crash.
Rins therefore lined up on pole, with Maverick Vinales - who had congratulated Rins following the first stoppage when he believed the race was over - second and Luis Salom third.
The latter pair had been the only men able to stay with Rins over the opening part of the race, as his unrelenting pace caused huge fractions. Jonas Folger in fourth was more than 15 seconds down the road when the race was stopped.
The final five laps therefore presented Vinales, Salom and the rest of the field a chance to snatch victory from Rins's grasp.
Salom came the closest, passing Rins on the first run down to Turn 1 and then trading positions with him several times over the closing stages.
Rins finally settled matters at the penultimate turn, and when Salom ran wide Vinales was also able to steal through and grab second, just over one quarter of a second down from Rins.
Folger came home fourth, a position he held almost exclusively throughout the race, caught between the faster lead trio and a slower, multiple-bike squabble behind.
Alex Marquez had been in a similar position in fifth, but a crash on the first lap of the restart put him out of the running and meant Miguel Oliveira and Jack Miller's scrap became one for fifth.
It was Oliveira who eventually got the better of it, although he had been trailing Miller as part of an eight-strong fight for sixth prior to the stoppage.
Zulfahmi Khairuddin took seventh ahead of Alexis Masbou, who had not even been part of the top 13 prior to the restart.
Results - 5 laps: (red flag/restarted) Pos Rider Team/Bike Time/Gap 1. Alex Rins Monlau KTM 11m26.535s 2. Maverick Vinales Laglisse KTM + 0.244s 3. Luis Salom Ajo KTM + 0.547s 4. Jonas Folger Aspar Kalex-KTM + 1.230s 5. Miguel Oliveira Mahindra + 8.276s 6. Jack Miller Caretta-RTG FTR-Honda + 8.603s 7. Zulfahmi Khairuddin Ajo KTM + 10.147s 8. Alexis Masbou Ongetta FTR-Honda + 12.037s 9. Brad Binder Ambrogio Suter-Honda + 12.263s 10. Jakub Kornfeil RW Kalex-KTM + 12.737s 11. Danny Webb Ambrogio Suter-Honda + 13.221s 12. Arthur Sissis Ajo KTM + 14.030s 13. Isaac Vinales Ongetta FTR-Honda + 15.822s 14. Efren Vazquez Mahindra + 16.593s 15. Niklas Ajo Tecno KTM + 21.094s 16. Juanfran Guevara CIP TSR-Honda + 21.205s 17. Philipp Oettl Paddock Kalex-KTM + 21.351s 18. Alessandro Tonucci Tasca Honda + 21.599s 19. Matteo Ferrari Ongetta FTR-Honda + 21.772s 20. Ana Carrasco Laglisse KTM + 22.003s 21. John Mcphee Caretta-RTG FTR-Honda + 23.267s 22. Francesco Bagnaia Italia FTR-Honda + 30.965s 23. Eric Granado Aspar Kalex-KTM + 31.591s Retirements: Lorenzo Baldassarri Gresini FTR-Honda 2 laps Alex Marquez Monlau KTM 2 laps Toni Finsterbusch Kiefer Kalex-KTM 0 laps Retired during first start: Romano Fenati Italia FTR-Honda Jasper Iwema RW Kalex-KTM Florian Alt Kiefer Kalex-KTM Niccolo Antonelli Gresini FTR-Honda Alan Techer CIP TSR-Honda