The six-time IndyCar Series champion and 2008 Indy 500 winner scorched around the 2.5-mile Indianapolis Motor Speedway with a flying lap of 229.107mph in the #9 Chip Ganassi Racing Honda.
Indy-only entry Marco Andretti got comfortable right out of the gate and delivered the second-fastest lap in the #98 Andretti Herta Honda that was just 0.121s off the mark set by Dixon.
Two-time Indy 500 winner Takuma Sato, also only contesting an Indy-only programme, was third at a distant 0.619s in the #75 Rahal Letterman Lanigan Racing (RLL) Honda.
Top Chevrolet runner Pato O’Ward (Arrow McLaren), was fourth at 0.718s behind, followed by RLL’s Christian Lundgaard in fifth (+0.9237s).
The ominous clouds held off the rain long enough for roughly 23 minutes of on-track activity before unleashing enough moisture to put an early end to the session.
With that, the morning session that was originally scheduled for two hours saw race control cancel the break and extended practice to the end of the day, weather permitting.
Only three no-tow speeds were recorded, with Team Penske’s Scott McLaughlin nailing the best pace at 219.656 mph. He was followed by the #60 Meyer Shank Racing entry of Felix Rosenqvist, who ran a best of 219.230mph. RLL’s Pietro Fittipaldi was third at 216.137mph.
Josef Newgarden, the reigning Indy 500 champion, saw a rough start to his defence after a technical issue was found with a bad sensor on his installation lap and was not able to get any running.
“We got an issue, we're diagnosing,” he added. “We just got a sensor that's off right now.”
Kyle Larson, the 2021 NASCAR Cup Series champion, began his Month of May quest at the Brickyard in 27th on the leaderboard, running only two installation laps as he got used to the systems of coming on and off pit lane in his #17 Arrow McLaren/Rick Hendrick Chevrolet.
“It's definitely good,” Larson said. “Even at this point, I've gotten more today than I thought I would.
“So just getting to leave the pit lane a couple times, it was good; all that. As we get to tomorrow, we get like a clean day of running, I'll be able to learn probably a lot. I would think so.
“Wish I would've got more laps there, but overall, I'm still just happy to be here and I think [IndyCar] said we have like 30-some more hours of practice, so hopefully that's enough time for me.”
Source: Autosport