Franchitti picked up the lead out of the final pit stop on Lap 173 -- relying on a double stint of the Firestone Firehawks (62 laps) - and held off Dan Wheldon by 0.0423 of a second for his third win of the season.
Power's No. 12 Verizon Team Penske crew had a fueling equipment issue on the same pit stop and he had to duck onto pit lane with five laps left for a splash. He was running fourth at the time but finished a season-low 16th.
Franchitti closed to 23 points of Power with three oval races left.
Marco Andretti led an Andretti Autosport trio in the top five with a season-best-tying third place. Ryan Hunter-Reay and Tony Kanaan followed. Helio Castroneves finished sixth and Justin Wilson advanced 16 positions to finish seventh.
Franchitti posted his 26th Indy car racing victory, tying Rodger Ward for 11th on the all-time list (USAC, CART, Indy Racing league sanction). Johnny Rutherford (27) is next.
Also on Aug. 28, James Hinchcliffe held off Pippa Mann by 0.0159 of a second - the third-closest margin of victory in Firestone Indy Lights history - to win the Chicagoland 100.
Mann, who led her first laps of the season in the No. 11 Sam Schmidt Motorsports car, recorded a career-best finish and led three Sam Schmidt Motorsports drivers across the line. Philip Major also posted a career best to finish third and series championship points leader J.R. Vernay was fourth.
Hinchcliffe, who started 13th, was driving the high line and caught Mann on Lap 66 following a Lap 63 restart. It was his third victory of the season (first on an oval).
