Ryan Hunter-Reay gave Michael Andretti's team its first win since June 2008 with an excellent performance in the Long Beach IndyCar race.
The American - who currently only has a part-time deal with Andretti Autosport and needs more funding to complete the season - led home Dreyer & Reinbold's Justin Wilson and points leader Will Power (Penske).
Hunter-Reay had run second behind Power initially, with Wilson tagging along behind them to make a three-car lead pack.
Power looked in control until lap 17, when his car briefly got stuck in first gear coming out of the final hairpin. By the time he was back up to speed, Hunter-Reay and Wilson had shot through into first and second.
With his car now fully functioning again, Power tried to get back in touch with the leaders by running longer before his first stop, but Hunter-Reay and Wilson remained out of reach.
Indeed by half-distance Hunter-Reay had also begun to drop Wilson, but the Dreyer & Reinbold driver got back in contention when the leader became stuck behind midfielder Alex Lloyd (Dale Coyne Racing).
It took five laps before Hunter-Reay was able to muscle past Lloyd, and when Wilson tried to do likewise, the Dale Coyne Racing driver turned across the front of Wilson's car and wiped off half its front wing.
Wilson was able to make his final pitstop immediately, but the wing change meant he fell to third behind Hunter-Reay and Power when the stops were complete for the day.
That incident allowed Hunter-Reay to make a break, and even though the field was bunched up under yellow when Conquest driver Mario Romancini's attempt to pass Graham Rahal (Sarah Fisher Racing) took both into the Turn 1 tyres, Hunter-Reay remained totally in control.
With the lapped cars of Raphael Matos and Takuma Sato (who had also tangled with Lloyd earlier) as a cushion behind him at the restart, Hunter-Reay quickly established a 5s lead and held it to the flag, to claim his first win since Watkins Glen in 2008 and to give team boss Andretti his first victory since taking full control of the squad over the winter.
Wilson pounced on Power to reclaim second with a brilliant dive at Turn 1 just after the green, and while he could not catch Hunter-Reay, the Briton had no trouble resisting the points leader's retaliation attempts, as Penske was defeated for the first time in 2010.
Ganassi's Scott Dixon gained ground in the pits and beat Tony Kanaan (Andretti Autosport) to fifth.
Mario Moraes charged through the field from 15th on the grid to give KV a welcome sixth place, beating Penske's Helio Castroneves and Ryan Briscoe, the latter having lost positions at the final stops. Dan Wheldon (Panther) and Mike Conway (Dreyer & Reinbold) completed the top ten close behind, while Foyt's Vitor Meira beat muted reigning champion and 2009 winner Franchitti to 11th place.
There was only one major casualty among the frontrunners, as Alex Tagliani fell out of the top ten due to a refuelling glitch and then broke his Fazzt Dallara's suspension in a brush with Simona de Silvestro and Danica Patrick. Marco Andretti had earlier lost ground after damaging his Andretti Autosport car's front wing in a touch with Tagliani.
Pos Driver Team Gap
1. Ryan Hunter-Reay Andretti 85 laps
2. Justin Wilson Dreyer & Reinbold + 5.6031s
3. Will Power Penske + 8.5864s
4. Scott Dixon Ganassi + 10.6287s
5. Tony Kanaan Andretti + 11.7732s
6. Mario Moraes KV + 16.5171s
7. Helio Castroneves Penske + 16.8928s
8. Ryan Briscoe Penske + 18.2214s
9. Dan Wheldon Panther + 19.4575s
10. Mike Conway Dreyer & Reinbold + 19.9307s
11. Vitor Meira Foyt + 27.4005s
12. Dario Franchitti Ganassi + 28.1352s
13. Hideki Mutoh Newman/Haas/Lanigan + 28.6037s
14. Marco Andretti Andretti + 30.0120s
15. EJ Viso KV + 31.6182s
16. Danica Patrick Andretti + 32.1804s
17. Simona de Silvestro HVM + 33.1652s
18. Takuma Sato KV + 1 lap
19. Alex Lloyd Dale Coyne + 1 lap
20. Raphael Matos Luczo Dragon/de Ferran + 1 lap
Alex Tagliani Fazzt 65 laps
Graham Rahal Sarah Fisher 58 laps
Mario Romancini Conquest 58 laps
Bertrand Baguette Conquest 45 laps
Milka Duno Dale Coyne 10 laps