New Zealand's Scott Dixon finished fourth at Indy Toronto, surrendering the series lead to teammate Dario Franchitti
Scotsman Franchitti jumped well ahead on a restart with seven laps remaining and Australians Ryan Briscoe and Will Power chased over the last of 85 laps, finishing second and third respectively.
The victory put Franchitti two points ahead of Ganassi Racing teammate Dixon, with Briscoe 13 points back and Indianapolis 500 winner Helio Castroneves 78 off the pace.
Franchitti was slowed in the pits by a cracked wheel nut and fell back, but went into the pit lane just ahead of a crash by Rahal, allowing him to refuel and return in second place after the caution period.
On the restart, Franchitti moved past Brazil's Castroneves to reclaim the lead.
Castroneves and Canada's Paul Tracy crashed soon after, knocking out both contenders.
However, Dixon and his wife Emma can still smile, after welcoming a baby girl named Poppy last week.