Fresh from qualifying P5 for the Indianapolis 500, Fernando Alonso was back out on track on Monday and completed 122 laps at the famous oval.
The two-time World Champion was 12th fastest at the end of the three-and-a-half session with a best average lap speed of 226.147 mph, which was considerably slower than the 231.475 mph he posted in Sunday's qualifying session.
Top of the timesheets was ex-Formula 1 driver Max Chilton who recorded a best lap of 228.592 mph in a 108-lap session.
"The more laps you do around here, the more you learn," said Chilton. "I don't think anyone out there is overly happy with their car in race traffic. You keep trying to learn, trying to get it better.
"In clear air, I seem to be pretty competitive. In dirty air, I started to learn how to time the moves. This is going to be my second 500. I'm still learning but it's always nice to finish the day at the top of the time sheet."