It was a tough night for series points leader Will Power of Australia, who was running among the leaders when he abruptly went to pit road for an extra fuel stop with five laps left in the race. He finished 16th.
That's an ideal scenario for Scotland's Franchitti, who came into Saturday's race trailing Power by 59 points in the standings.
“I'm delighted,” Franchitti said in victory lane.
England's Dan Wheldon finished second, followed by Marco Andretti, Ryan Hunter-Reay and Tony Kanaan of Brazil.
Power's crew apparently didn't get enough fuel in the car to make it to the end of the race during their last scheduled pit stop. It certainly cost them a shot at a top-three finish; now his team has to hope it doesn't end up costing them the championship.
Power was gracious in a television interview after the race, noting that he still leads the points.
“That's racing,” he said.
Beginning with Chicagoland, the final four races of the season all are on oval tracks, and Power is considered a stronger driver on road courses than he is on ovals. So he was encouraged by his strong driving performance on Saturday, even if it didn't get him a good finish.
“I never thought I could race ovals like that,” Power said.
Power hardly was racing conservatively to protect his points lead, going three-wide for the lead with Wheldon and Andretti with about 50 laps to go.
With Power in the lead and Andretti stuck to his rear wing, Alex Lloyd spun out with 31 laps to go, bringing out a caution. That allowed all the leaders to make their final pit stop.
Franchitti's crew gambled by only taking fuel and opting not to change tires, gaining eight spots in the pits and sending him out in the race lead.
Power was second, but his crew knew right away that a mechanical issue might have prevented them from getting enough fuel in the car to make it the rest of the way.
Danica Patrick finished 14th as one of five female drivers in the race.
It was a strong outing for Sarah Fisher, who briefly led near the race's halfway point and was able to hang in the top five for several laps. She slipped back in the pack when she had to make a pit stop on lap 113 and finished 15th.
Milka Duno finished 19th, Simona de Silvestro finished 23rd and Ana Beatriz finished 24th.
It was a frantic night of racing often featuring a large pack at the front of the pack running inches apart at more than 200 mph.
But it might be the last time IndyCar puts on its usual good show at the 1.5-mile track on the outskirts of Chicago, at least for the foreseeable future.
Earlier Saturday, IndyCar CEO Randy Bernard said he was in meetings with the track's management but wasn't sure anything could be worked out for next season. Bernard said the Milwaukee Mile could rejoin the IndyCar schedule instead.
Attendance figures weren't immediately available for Saturday's race, but there were significant bare spots in the grandstands.
