Ryan Hunter-Reay fought off Scott Dixon to become the first non-Penske driver to win an IndyCar race at Barber Motorsports Park.
Hunter-Reay was in contention throughout the race, but he moved into the lead for the final time when he took advantage of his softer red tyres to pass primary tyre-shod Helio Castroneves with 15 laps to go.
Castroneves immediately fell victim to Dixon as well, and what had been a 1.2-second advantage to the American was swiftly eroded as Dixon closed him down.
But he was never able to find a way past and Hunter-Reay crossed the line 0.6s clear, consigning Dixon to second for the fourth year in a row.
Hunter-Reay had to survive a couple of potential derailments en route to Victory Lane. He had found himself behind an out-of-sequence Will Power during his second stint, and despite being on the better tyres, was not able to pass the Australian until he finally pitted.
Shortly afterwards he made contact with Castroneves just after the Brazilian passed him, but escaped damage.
"Helio and I always race clean," Hunter-Reay said. "I had a little bit of contact with him when I just couldn't slow the car down. But when we were on the new reds and he was on the blacks [at the end], he was a sitting duck."
Castroneves was third ahead of Charlie Kimball, who was one of the surprise performers of the weekend.
That was partly due to him getting more life out of the red tyres than he had expected to, but his highlight-reel moment came with a lurid pass on Power late in the race.
Power had already had his share of drama by that point, having run wide on the opening lap and dropped seven places.
The Penske team switched to a two-stopper in an effort to salvage something, but the fact that most of the race ran under green forced Power to spend too long fuel saving to make up any ground. He ran out of E85 immediately after crossing the finish line.
Compared to some of the series' other big names, Power's problems were nothing.
St Petersburg winner James' Hinchcliffe suffered a broken wheel in an opening-lap clash with Oriol Servia and Graham Rahal, leaving him to watch the rest of the race from behind a safety wall.
It was also a tough day for Dario Franchitti, who retired with a broken header, although the Scot took some solace from the fact that he had moved well into the top 10 from his starting position of 17th at the time the problem struck.
AJ Allmendinger's single-seater return ended with him finishing 19th after running in the top 10 early on.
Results - 90 laps:
Pos Driver Team/Car Time/Gap
1. Ryan Hunter-Reay Andretti Dallara-Chevy 1h52m04.5450s
2. Scott Dixon Ganassi Dallara-Honda + 0.6363s
3. Helio Castroneves Penske Dallara-Chevy + 17.6821s
4. Charlie Kimball Ganassi Dallara-Honda + 20.6166s
5. Will Power Penske Dallara-Chevy + 26.6469s
6. Simon Pagenaud Schmidt Dallara-Honda + 27.2995s
7. Marco Andretti Andretti Dallara-Chevy + 27.7175s
8. Justin Wilson Coyne Dallara-Honda + 30.5504s
9. Josef Newgarden Fisher Dallara-Honda + 41.1029s
10. Tristan Vautier Schmidt Dallara-Honda + 50.6449s
11. Alex Tagliani Herta Dallara-Honda + 58.0458s
12. EJ Viso Andretti Dallara-Chevy + 1m01.4334s
13. Tony Kanaan KV Dallara-Chevy + 1m01.6834s
14. Takuma Sato Foyt Dallara-Honda + 1m03.1151s
15. Oriol Servia Panther/DRR Dallara-Chevy + 1m03.1495s
16. Sebastien Bourdais Dragon Dallara-Chevy + 1m07.6880s
17. JR Hildebrand Panther Dallara-Chevy + 1m09.7447s
18. Simona de Silvestro KV Dallara-Chevy + 1m09.9130s
19. AJ Allmendinger Penske Dallara-Chevy + 1m11.0558s
20. Sebastian Saavedra Dragon Dallara-Chevy + 1m11.6523s
21. Graham Rahal Rahal Dallara-Honda + 1m14.0385s
22. Ed Carpenter Carpenter Dallara-Chevy + 1 lap
23. James Jakes Rahal Dallara-Honda + 4 laps
Ana Beatriz Coyne Dallara-Honda 65 laps
Dario Franchitti Ganassi Dallara-Honda 42 laps
James Hinchcliffe Andretti Dallara-Chevy 3 laps