The Australian clocked a session-best 227.026 mph lap late on Wednesday to be the only driver in the 227 mph bracket.

Lightning near the speedway brought proceedings to a close with 30 minutes left on the clock.

Team Penske stablemate Josef Newgarden, a two-time Indianapolis 500 winner, was second with a 226.971 mph that stood atop the pylon for much of the day.

Chip Ganassi Racing’s Alex Palou and Scott Dixon were third and fourth respectively while Scott McLaughlin bookended the top five for Team Penske.

In all, drivers got roughly three hours of on-track running after proceedings were delayed by rain.

The day was incident-free, though there were curious scenes for IndyCar newcomers Prema who spent the lion’s share of the day parked up.

Callum Ilott and Robert Shwartzman and were last and second-to-last, respectively. Ilott ran 16 laps with a 217.189 mph effort his best of the day. Shwartzman, meanwhile, cut just six laps with a 217.836 mph best.

Of the no-tow runners, Andretti Global’s Kyle Kirkwood led the way on a 219.497 mph lap ahead of Newgarden and surprise packet Jacob Abel for Dale Coyne Racing, who could make his Indy 500 debut this year as long as he qualifies.

Practice is scheduled to continue on Thursday at 2:30am AEST.

Results: 109th Indianapolis 500, Practice 1