Esteve Rabat took his second win of the Moto2 season at Indianapolis as the Championship reconvened after a summer break, with Takaaki Nakagami and standings leader Scott Redding completing the podium.
Redding's title rival Pol Espargaró finished fourth as the Brit managed to edge his advantage at the top of the Championship to 26 points over his Spanish adversary, whose team-mate Rabat powered to the win.
Redding had led at the start of the race but Nakagami got past, and Rabat's charge came in the final third of the race as he pulled himself through from fifth on lap 17 to finish first by the race-ending 25th lap. The Spaniard beat Nakagami to first by 0.7s with Redding managing to hold off Espargaró for third.
Moto3: Rins holds of Márquez for the win
In the Moto3 race it was a close encounter between team-mates Alex Rins and Alex Márquez for the victory, with the former taking it and in the process closing the gap to Championship leader Luis Salom.
Red Bull KTM Ajo rider Salom started from 10th on the grid after a huge crash in qualifying, but managed to fight his way to fifth to limit the damage to his lead at the top of the standings.
Up front Rins took his third win of the season by just 0.177s from Márquez, younger brother to MotoGP's Marc, with Maverick Viñales taking third. Viñales lies second in the Championship and now just nine points off Salom with Rins third and a further seven points down.
The Moto2 and Moto3 riders now head directly to Czech Republic for the second in a sequence of three back-to-back Grands Prix.