Simon Pagenaud marched to a fourth win of the season at Mid Ohio after a pair of cautions swung the advantage to a handful of different drivers.
Pagenaud had been leading Team Penske team-mate Will Power when the first caution hit at lap 15 of the 90.
A tangle between Helio Castroneves and Scott Dixon into the Keyhole hairpin brought the yellow flags out, and handed the advantage to Mikhail Aleshin and the other drivers who had already pitted on the undercut strategy.
After the pitstops cycled out Aleshin looked like he would take a maiden series win, but the second caution caused by Jack Hawksworth slamming into the Turn 1 barriers on lap 60 proved his undoing.
As the final pit window opened following Hawksworth’s crash, the whole field other than Dale Coyne Racing team-mates Conor Daly and RC Enerson took to the pits.
Aleshin’s Schmidt Peterson mechanics waved him out of his box but the incoming Josef Newgarden who occupied the pitbox in front meant Aleshin careered into the Ed Carpenter Racing driver, and put him out of contention when he had to pit again one lap later for a new wing.
That left Daly gunning it from the front on the restart in a bid to make his four-stop strategy work, but with limited fuel and older tyres he had to pit in the dying laps, swinging the advantage and the race win back to Pagenaud.
The championship leader eventually crossed the line 4.1 seconds ahead of Power.
Carlos Munoz completed the podium, taking advantage of the same undercut strategy as Aleshin and crossing the chequered flag as the highest Honda-powered Dallara.
Graham Rahal and James Hinchcliffe did well to finish in fourth and fifth respectively after Takuma Sato and Sebastien Bourdais - who had been running ahead – touched with just three laps to go.
A final splash and dash meant Daly picked up respectable points in sixth.
It was an anonymous race for both Juan Pablo Montoya and Tony Kanaan who could only manage 12th and 13th respectively.
Enerson had been running well in his IndyCar debut before the engine cutting out on one of his pitstops meant he finished 20th.