Helio Castroneves was leading with less than 25 laps to go when his rear wing collapsed, throwing him into the wall. Then team mate Sam Hornish slowed as his wing bent out of position, though he was able to finish the race.
Indy 500 winner Dario Franchitti finished second, making an Andretti-Green one-two, with Dan Wheldon third.
Pole sitter Castroneves led the early running until the first caution period on lap 23. Most of the front runners pitted except for Buddy Rice, who took the lead from Kanaan, Castroneves and Hornish.
The two Penskes swapped positions before Castroneves broke ahead again, passing Kanaan then inheriting the lead from Rice, whose tyres went off after sixty laps. Rice tumbled down the field with Kanaan, Wheldon, Franchitti and Scott Dixon passing him.
Wheldon worked his way up to second behind Castroneves but caused a caution period when he brushed wheels with Danica Patrick, sending the Andretti-Green racer off the track. Patrick confronted Wheldon in the pits after the race – but Wheldon appeared to do his best to ignore her.
Another debris caution followed shortly afterwards and speedy pit work by team Ganassi propelled Wheldon into the lead. He rapidly pulled away from Castroneves and had a 1.4s lead at two-thirds distance. Franchitti ran third ahead of Hornish, Kanaan and Dixon.
Tomas Scheckter joined him in retirement shortly after as his car stopped at the end of the pit lane. Scheckter had made a stunning start, passing five cars around the outside on the first lap to take eighth. Before his retirement his race was spoiled on lap 83 when he stalled in the pits.
When the race went green again on lap 169 Wheldon struggled for pace and was quickly passed by Castroneves, Hornish and Kanaan. Vitor Meira, who had taken third, also struggled and lost four places.
On lap 202 Castroneves’ rear wing suddenly collapsed and threw him into the barrier along the pits. The Brazilian was unhurt – but it pointed towards a problem with the Penskes that Hornish’s car would soon exhibit. Meanwhile, Kanaan moved up into the lead in Castroneves’ place.
No sooner had the race restarted on lap 209 there was another car in the wall – Marco Andretti’s, who ran wide in the first corner and understeered straight into the barrier. Another poor result for the highly rated rookie in his difficult second season.
There were 11 laps remaining when the race got going again and once more Wheldon seemed to be struggling. He lost third place to Franchitti and had to defend carefully from team mate Dixon.
Hornish’s problem became apparent with five laps to go when it appeared that his rear wing was askew. He lost second to Franchitti before passing through the pit lane, but the team elected he should continue to collect as many points as possible.
That left the two Andretti-Green cars up front with no-one to challenge them. Kanaan took the win to ease some of the disappointment of his Indianapolis misfortune, while a delighted Franchitti now leads the title race.
It’s a British one-two at the top of the table with Franchitti on 221 points and Wheldon 218. Dixon – who has finished every race this year in the top five – has 216.
Kanaan moves up to fourth ahead of the two Penske drivers. The duo will rue the precious points lost to unreliability today – at least until their chance to make amends at Texas next week.