Spain's Marc Marquez claimed his second successive MotoGP victory as he led home defending world champion Jorge Lorenzo in Austin, Texas.
The Honda rider backed up last weekend's victory in Argentina, leading from start to finish to extend his lead at the top of the title standings.
Valentino Rossi and Dani Pedrosa crashed out, as did British duo Cal Crutchlow and Bradley Smith.
Another Briton, Scott Redding, came home sixth.
Andrea Iannone was third for Ducatti at the Circuit of the Americas.
Smith and Crutchlow both slid off at the same corner on the same lap, with Smith later blaming oil on the circuit.
Marquez's win was his fourth in a row in Texas.
He said: "I'm really happy, especially as I rode a really good race.
"The race wasn't much fun but we got 25 points and that is the most important thing."
Marquez leads Lorenzo by 21 points at the top of the standings, with Rossi third, a further 12 points back
1. Marc Marquez (Spain) Honda 43:57.945
2 Jorge Lorenzo (Spain) Yamaha +6.107
3. Andrea Iannone (Italy) Ducati +10.947
4. Maverick Vinales (Spain) Suzuki +18.422
5. Aleix Espargaro (Spain) Suzuki +20.711
6. Scott Redding (Great Britain) Ducati +28.961
7. Pol Espargaro (Spain) Yamaha +32.112
8, Michele Pirro (Italy) Ducati +32.757
9. Hector Barbera (Spain) Ducati +34.592
10. Stefan Bradl (Germany) Aprilia +40.211