Marco Simoncelli became the first and last winner of a 250cc Indianapolis Grand Prix, following last year's storm-cancelled event and prior to the introduction of Moto2, with a 1.943sec victory over world championship leader Hiroshi Aoyama.
Simoncelli and Aoyama reached the front of the pack within four laps while Alvaro Bautista, who began round eleven 12 points behind Aoyama, once again made a sluggish start.
The Spaniard finished lap one in tenth place before rising to fourth - behind Simoncelli, Aoyama and pole sitter Mike di Meglio - on lap 8 of 26.
Aoyama continued to match Simoncelli's Metis Gilera through the middle stages, while Bautista took third from Aspar Aprilia team-mate di Meglio with ten laps to go. The 2010 Suzuki MotoGP rider then faced a 1.5sec gap to Aoyama, which he was unable to bridge.
A scare for Aoyama with five laps to go gave Simoncelli vital breathing room and the Italian won his fourth race of the year by just under two-seconds from the Scot Honda rider.
Simoncelli thus became the first rider this season to take back-to-back wins, and has closed from 32 points to 27 points from Aoyama with five rounds to go. Bautista remains second, but is now 16 points from the Japanese.
Class rookie di Meglio, who survived a near highside and contact with Aoyama early in the race, confirmed fourth.
Jules Cluzel, fastest in the wet on Friday, produced a further surprise by leading the first three laps of the race before a spectacular fall from fourth on lap 8 left the Frenchman - second at the Qatar season opener - punching the grass in frustration.
Race results - Indianapolis:
1. Simoncelli (Gilera)
2. Aoyama (Honda) +1.943sec
3. Bautista (Aprilia) +4.661sec
4. di Meglio (Aprilia) +12.776sec
5. Locatelli (Gilera) +15.475sec
6. Barbera (Aprilia) +19.471sec
7. Pesek (Aprilia) +22.682sec
8. Faubel (Honda) +32.809sec
9. Luthi (Aprilia) +49.321sec
10. Abraham (Aprilia) +49.845sec