Alexander Rossi dominated proceedings at Road America to score his second victory of 2019 in an even more emphatic manner than his Long Beach win earlier in the year.
The Andretti driver passed pole sitter Colton Herta at the start and controlled the race from that point on.
He finished almost half a minute clear of second-placed Will Power.
Power: “I couldn’t see Alex, he was just gone.”
Josef Newgarden followed Penske team mate Power home in third place, the pair fighting-wheel-to-wheel into Canada corner at one stage.
The Penske drivers were the only Chevrolet-powered cars in the top 10.