Grosjean had a small moment in Turn 6, which resulted in his Honda-powered Andretti Autosport entry to be caught by the surging Juncos Hollinger Racing Chevrolet of Ilott.
The British driver closed up to Grosjean and darted to the left for a move entering Turn 7, but the two hit flush wheel-to-wheel, which sent Ilott off course and through maze of dirt that wraps around the 12-turn, 1.964-mile road course.
“Yeah, I didn't see him,” Grosjean told Autosport. “I was looking on the right-hand side. It was a traffic jam. He went on the left and I'm sorry. I just didn't.
“I was looking right and he was left. I think it is what it is. I don't know why he tried to go through at that point, but I was struck by #27 [Kyle Kirkwood]. I didn't see him.”
Grosjean put down a session-most 30 laps, ending up 16th overall and 0.4808s behind pace-setter Scott McLaughlin’s mark of 58.1516s.
Ilott, who ended up 20th and 0.7155s behind, had a different view of the incident.
“I don't what he is doing,” Ilott said. “He was driving off the track at the time. I think he knew I was there for a whole lap and defended into the corner. I don't know. I'm not too bothered by it. It's just a bit stupid really.
“I think that's a standard saying, 'You don't see anyone.' Whatever. It is practice. I don't really care, but it's just a bit unnecessary and especially when we're coming to the chequered, like 500 metres later. It's not racing for the next lap.
“He'd run off wide, so I was just putting the car there.”
When asked how the car feels following the session, the Briton replied: “Just people like him ruining every single run. I've had two clear laps on my new tyres across three runs. It’s tough with the traffic. It is what it is. It's the same for everyone.”
