Ryan Hunter-Reay won the 2012 IndyCar championship after rival Will Power crashed out of a dramatic season finale at Fontana, won by Ed Carpenter.
The championship battle was turned on its head on lap 54, just as the title protagonists encountered one another on the track for the first time.
Hunter-Reay was running a high line and Power tried to go underneath him to take the position but dropped the rear, snapping his car around and putting him into the wall. Hunter-Reay was fortunate not to be caught up in the accident as well, with Power's car barely missing him on its journey towards the barriers.
Despite the severity of the damage to Power's car, Team Penske committed as many personnel as it could muster to patching it back together and somehow managed to get it back onto the track.
Power, now more than 60 laps down, staggered around in a car entirely bereft of any sort of set-up for just long enough to complete 12 laps and gain another position and another two points, meaning that Hunter-Reay now needed to finish fifth rather than sixth to secure the crown.
The Andretti Autosport driver had spent most of the second half of the race just one position shy of where he needed to be when Alex Tagliani, who had been fighting for the lead, suffered an engine failure, bringing out the yellows and promoting Hunter-Reay into fifth and giving him a one-point lead over Power.
An aggressive restart allowed Hunter-Reay to climb as high to third when Tony Kanaan lost control and crashed on lap 242. Rather than cleaning up the wreckage under a yellow, race director Beaux Barfield threw a red flag, setting up a six-lap sprint to the finish line - a decision that caused some dismay on the Andretti pit wall.
Shortly after the restart, Hunter-Reay found himself under pressure from Scott Dixon, who he let past, and Takuma Sato, who he battled for a couple of laps before the Japanese driver lost control and crashed on the second-last lap, sealing Hunter-Reay's triumph by moving him up to fourth and bringing the race to an end.
"I cannot believe we are IndyCar champions," he said. "I cannot believe this. That last red flag got the nerves going. It hasn't sunk in yet. We put a lot of hard work in and we've got the right people surrounding us."
Carpenter took the race win after fighting Dario Franchitti over the closing laps.
"We were really good early, kind of struggled through the middle and the team made some adjustments and we got back in," said Carpenter, who had earlier distinguished himself by catching a lurid slide towards the wall with 30 laps remaining.
Dixon completed the podium ahead of Hunter-Reay and Helio Castroneves, who had gambled on an extra stop at the final restart to throw on a new set of tyres and could potentially have gained another position or two had the race run full distance.
Early race leader JR Hildebrand's evening was ruined when he glanced the wall at Turn 4 and damaged his suspension, costing him two laps in the pits while his car was repaired.
Rubens Barrichello was also in the frame for a good result, running as high as third before his engine went up in flames just before the halfway mark.
Results - 250 laps: Pos Driver Team/Car Time/Gap 1. Ed Carpenter Carpenter Dallara-Chevy 2h57m36.6565s 2. Dario Franchitti Ganassi Dallara-Honda + 1.9132s 3. Scott Dixon Ganassi Dallara-Honda + 2.6091s 4. Ryan Hunter-Reay Andretti Dallara-Chevy + 3.0477s 5. Helio Castroneves Penske Dallara-Chevy + 4.1933s 6. Graham Rahal Ganassi Dallara-Honda + 5.4381s 7. Takuma Sato Rahal Dallara-Honda + 1 lap 8. Marco Andretti Andretti Dallara-Chevy + 1 lap 9. Katherine Legge Dragon Dallara-Chevy + 1 lap 10. Charlie Kimball Ganassi Dallara-Honda + 1 lap 11. JR Hildebrand Panther Dallara-Chevy + 2 laps 12. James Jakes Coyne Dallara-Honda + 2 laps 13. James Hinchcliffe Andretti Dallara-Chevy + 3 laps 14. Wade Cunningham Foyt Dallara-Honda + 4 laps 15. Simon Pagenaud Schmidt Dallara-Honda + 4 laps 16. Josef Newgarden Fisher Dallara-Honda + 6 laps 17. Ryan Briscoe Penske Dallara-Chevy + 6 laps 18. Tony Kanaan KV Dallara-Chevy + 10 laps* 19. Oriol Servia Panther/DRR Dallara-Chevy + 19 laps Retirements: Alex Tagliani Herta Dallara-Honda 229 laps Sebastian Saavedra AFS/Andretti Dallara-Chevy 118 laps Rubens Barrichello KV Dallara-Chevy 107 laps Justin Wilson Coyne Dallara-Honda 80 laps Will Power Penske Dallara-Chevy 66 laps EJ Viso KV Dallara-Chevy 65 laps Simona de Silvestro HVM Dallara-Lotus 16 laps * Not running at finish