Scott Dixon was awarded victory at Edmonton after Helio Castroneves had the win taken away, having been adjudged to have blocked his teammate Will Power.
Castroneves crossed the line first, having snatched the lead from Power late on. But the checkered flag was held back for Dixon, who had also slipped past Power, as the officials stopped scoring Castroneves on the final lap as a punishment for an allegedly illegal defensive move, dropping him to 10th.
Drivers were warned by series Chief Steward Brian Barnhart during the pre-race drivers meeting on blocking: "You have plenty of options on where to put your car and we should not have any defending or blocking. Again, we will be visually dividing the braking point through the entry into the corner in half. You can only be on the inside half if you are attempting to pass someone. If you are on the inside half because you are under attack from someone else, it is blocking. Don't move your car in reaction to a following car and don't impede the progress of a car with a run on you."
"Brian always says that if you're blocking going into any corner and you are on the right side – especially into Turn 1, you're going to get a penalty," related Dixon. "We get told every week, so you could see something was going to happen.
"The Target car was pretty loose," he added. "I can't believe that we won."
Indeed, Power seemed in complete control for most of the race, holding a secure lead over Castroneves. Their teammate Ryan Briscoe even briefly gave Penske a 1-2-3 formation by passing Ganassi duo Dario Franchitti and Dixon in quick succession near the end of the first stint, though they would return the favor and demote him back to fifth shortly before the final stops.
It was just after that final round of pit visits that Castroneves surged onto Power's tail, the Australian having stayed with the harder black tires at the stop where his teammates and Ganssi took the faster but fragile reds. Suddenly, Power was struggling to hold Castroneves off and, with 19 laps to go, the Brazilian swept past into Turn 1, then left Power to fend off Dixon.
A late yellow gave Power one last shot at attacking Castroneves, but his attempt to drive around the outside of the leader at Turn 1 saw him lose second to Dixon as he slid wide. It was while fending off Power at this point that Castroneves was judged to have blocked his teammate unfairly. The decision left Castroneves both distraught and enraged as he realized the win had been taken away.
"I never moved my line. I actually did move him outside," claimed Castroneves. "When you go side by side like that with your teammate and they just take it away from you, it's just absurd."
Power insisted that he had been blocked, but didn't seem eager to make a big deal out of it. "I got a run on him and he blocked me. I would say a black flag is a pretty harsh penalty, but it is what it is," declared the Australian. "It was just one of those racing things. When you're leading on the last restart, you want to keep the lead."
Franchitti and Briscoe completed the top four, with Ryan Hunter-Reay snatching fifth for Andretti Autosport in a late battle with Paul Tracy. The Canadian hero charged through to an excellent sixth for KV – which got all four of its cars into the top 10, with Takuma Sato, Mario Moraes and EJ Viso filling seventh to ninth places.
Tracy made rapid progress from his 15th place on the grid, although his early charge did involve contact that ruined De Ferran Dragon driver Raphael Matos' race. He later overtook Ryan Hunter-Reay (Andretti Autosport) for sixth midrace, but lost out to the American again while trying to pass Briscoe at the final restart.
Sixth could easily have gone to the hugely impressive Simona de Silvestro of HVM, who was fighting for the position until pushed into a spin by Viso. She recovered to 11th before her car expired late on.
Andretti's Tony Kanaan came through from the back row of the grid to 12th, although his race also involved contact along the way, as a brush with Alex Tagliani sent the Fazzt entry spinning into Conquest's Mario Romancini.
Other drivers in trouble including the Dreyer & Reinbold duo, who both had to pit for suspension repairs, and Hideki Mutoh (Newman/Haas), who lost a lot of ground with a midrace spin.
Pos Driver Team Gap
1. Scott Dixon Ganassi 95 laps
2. Will Power Penske + 2.6688s
3. Dario Franchitti Ganassi + 3.2831s
4. Ryan Briscoe Penske + 8.8652s
5. Ryan Hunter-Reay Andretti + 11.1482s
6. Paul Tracy KV + 11.9091s
7. Mario Moraes KV + 16.9015s
8. EJ Viso KV + 18.2206s
9. Takuma Sato KV + 21.5880s
10. Helio Castroneves Penske + 42.6011s
11. Marco Andretti Andretti + 1 lap
12. Tony Kanaan Andretti + 1 lap
13. Raphael Matos De Ferran Dragon + 1 lap
14. Bertrand Baguette Conquest + 1 lap
15. Danica Patrick Andretti + 1 lap
16. Vitor Meira Foyt + 2 laps
17. Hideki Mutoh Newman/Haas + 2 laps
18. Alex Lloyd Dale Coyne + 3 laps
19. Tomas Scheckter Dreyer & Reinbold + 5 laps
20. Dan Wheldon Panther + 5 laps
21. Justin Wilson Dreyer & Reinbold + 7 laps
Simona de Silvestro HVM 87 laps
Alex Tagliani Fazzt 52 laps
Mario Romancini Conquest 52 laps
Milka Duno Dale Coyne 4 laps