Dixon was knocked into a spin by a slowing Buddy Rice on the penultimate lap and appeared to deliberately steer his car into Franchitti’s.
Franchitti managed to limp home sixth to take a three point lead in the championship with one round left to run.
Helio Castroneves started from pole position, setting a new record for the most in a single IRL season with his seventh of the year. He held onto the lead at the start ahead of Dario Franchitti, with Tony Kanaan passing Scott Dixon for third.
Halfway around the first lap Marco Andretti dived past Ryan Hunter-Reay for fifth, but he could keep up with the top four and was 13.6s behind Dixon by lap 17. The luckless Hunter-Reay later retired after a mechanical failure at his first pit stop.
The top four hit traffic on lap 20 and all bar Castroneves reacted by diving for the pits right away. They resumed in the same order, but Castroneves fell behind them all after postponing his stop to lap 26.
The first caution period came on lap 28 when Ed Carpenter stopped on track. The race resumed three laps later but went into caution once again after a four car pile-up. Sam Hornish Jnr tapped Sarah Fisher into a spin, who was collected by Vitor Meira. Danica Patrick braked in avoidance and was hit from behind by Darren Manning, who spun her into the barrier.
The race restarted once more on lap 43 with Franchitti leading Kanaan and Dixon. But four laps later Patrick knocked Scott Sharp into a spin, triggering another caution period.
This time Buddy Rice, Patrick and Dan Wheldon stayed out and moved to the front of the pack ahead of Kanaan (who accidentally short-fuelled due to an equipment problem), Franchitti, Dixon and Castroneves.
Another brief restart followed before Carpenter spun and caused a fourth caution on lap 55. Rice, Kanaan and Castroneves all pitted leaving Patrick in the lead from Wheldon, Franchitti and Dixon.
Once the race began again Kanaan quickly made progress up to fifth behind Dixon. Wheldon and Patrick pitted under green conditions shortly before the fifth caution of the day. This was caused by Castroneves, who tried an extremely optimistic move on Tomas Scehckter that put both of them into the barrier.
The drivers hurried their final pit stops, suspecting that the race would stop at two hours instead of reaching the planned distance. Kanaan and Rice gambled on staying out and took up first and second followed by Dixon, who took on less fuel than Franchitti, the Briton falling to fifth behind Patrick.
Shortly after the race got going again Patrick moved aside to let her team mate through, and soon they formed a four-car chain for the lead.
Kanaan and Rice were clearly nursing their fuel loads and this allowed Franchitti to take a look at Dixon. The New Zealander appeared to feign a defence and word quickly came from the stewards that if he did it again he’d be in trouble.
By the penultimate lap Rice was driving conspicuously slowly. So when Dixon got fully alongside him to pass it was quite inexplicable that Rice should have turned in the way he did.
It was the catalyst for the most controversial accident of the season so far. The spinning Dixon appeared to deliberately steer his car to pin Franchitti’s against the wall and ensure he did not progress.
A final caution was thrown and while Franchitti was pulled out of the barriers Kanaan took the win for Patrick. By the time Franchitti limped around to the flag he had fallen to sixth behind Wheldon, Darren Manning and Kosuke Matsuura. Rice and Dixon were classified seventh and eighth.
A furious Michael Andretti claimed Dixon’s had deliberately steered to hit Franchitti. But the Briton exonerated his rival. Franchitti’s quick thinking actually means he has moved back ahead in the title race by three points ahead of next week’s decider at Chicagoland.
It’s a race not to be missed.