Franchitti bumped Power's car into a spin in Turn 3 on the 57th of 85 laps. The Scotsman then drove his undamaged Target Ganassi Racing entry to the third win of his career on the bumpy street circuit near downtown Toronto.
Power and Team Penske were left fuming and facing a 58-point deficit to their rivals after 10 of 18 races.
"I've always raced him clean and he always races me dirty," Power told reporters in pit lane. "He did the same at St. Pete -- he drove me into the wall and I didn't say anything. He did it again today.
"I'm disappointed in Dario," he added. "He's the guy that mouths off about everyone and whines about everyone, and he's the guy racing dirty who never gets a penalty from INDYCAR. It's just not right."
INDYCAR stewards Al Unser Jr., Tony Cotman and Bill Van de Sandt reviewed the incident and consulted with chief steward Brian Barnhart, who determined that the Franchitti/Power clash was a simple racing incident. However, it was mistakenly stated on the Versus television broadcast that Franchitti would be brought in for a drive-through penalty for avoidable contact, leading to plenty of pit-lane confusion.
Power later was spun out again by Alex Tagliani and wound up finishing 24th. After leading the Izod IndyCar standings by 21 points following the Texas Twin 275s a month ago, Power has ceded 76 points to Franchitti.
And the Australian's frustration is starting to boil over.
"Not good for the Verizon car," he said. "Two races in a row we're out.
"I'm so disappointed in [Franchitti]," he repeated. "He's twice done me dirty on the track. It's just unbelievable. And then INDYCAR won't penalize them because Chip Ganassi goes up there and gives it to them. It's just wrong."
Naturally, the contretemps with Power was the subject everyone wanted Franchitti to talk about after the race. Franchitti was taken aback when he was told Power called him a dirty driver.
"I think that's a slight exaggeration," Franchitti said. "We've had contact once, and that was today.
"I watched it on TV, and it was a racing incident at best," Dario continued. "I think I'm known in the paddock as not someone who drives dirty, so I'm not really sure what he's talking about."
Franchitti said he raced side by side through Turn 3, on the inside and the outside of several other competitors. But he claimed Power didn't leave him enough room.
"I understand he's upset, but hopefully when he cools down he'll reassess that," Franchitti said.
The championship leader was correct when he called the 25th running of the Toronto street race "an absolute wild one." There were six full-course cautions, all for incidents of contact.
I watched it on TV, and it was a racing incident at best. I think I'm known in the paddock as not someone who drives dirty, so I'm not really sure what he's talking about.
”-- Dario Franchitti on Will Power's accusation that he is a dirty driver
Power wasn't the only one who left Toronto unhappy. Scott Dixon completed a 1-2 finish for the Target Team, but he wasn't happy about the way his satellite teammate Graham Rahal raced him late in the contest.
Rahal, trying to stretch fuel and tires for 44 laps, lost second place to Dixon in Turn 3 on a Lap 80 restart, then got punted into a spin in the same corner by third-place finisher Ryan Hunter-Reay.
"I just got hit," fumed Rahal. "I'm really ticked and I'm trying to control my emotions. That's not like Hunter-Reay, but I guess some people strap on their helmets and lose their brain."
Andretti recovered to finish fourth, an excellent result after he qualified 20th.
"Marco is an aggressive driver, but he's always raced me clean," Servia said. "But today, I think he just had a bad sleep or something."
Franchitti's fourth win of the 2011 season (and 30th of his career, moving him ahead of Rick Mears into solo ninth place on the all-time
list) put him into a commanding championship lead by recent IndyCar Series standards.
But the Scotsman knows that any weekend can produce a 41-point swing.
"Anything can happen," Franchitti said. "My guys in the pit cart had a big hand in this one, changing the strategy a bit by calling me into the pits early for my first stop when Will and Scott were being held up in traffic.
"I'm certainly not thinking about the points lead at this stage of the season," he added. "It's immaterial until the last race."
John Oreovicz covers open-wheel racing for ESPN.com.