American Josef Newgarden has driven away to his fourth IndyCar series victory of the season at Gateway Motorsports Park, extending his series lead over Kiwi Scott Dixon.
Dixon, driving for the Chip Ganassi team, finished 0.6850 seconds behind Newgarden in second and now has just two races remaining from the 17-race schedule to close the gap on the 26-year-old Team Penske driver from Tennessee.
"I guess that's the best we could have hoped for," Dixon said. "It's was definitely going to be a tough race for us, but the car was actually very good.
"I think we had a better mechanical grip than the group we were racing with and especially toward the end of the run."
Frenchman Simon Pagenaud was third, followed by Helio Castroneves and Conor Daly.