Callum Ilott is staking his claim to “super-sub” status in the NTT INDYCAR SERIES after leading the first session of the NTT INDYCAR SERIES Open Test on Saturday at The Thermal Club.

British driver Ilott, substituting for the injured David Malukas in the No. 6 Arrow McLaren Chevrolet, jumped to the top of the time sheets with a top lap of 1 minute, 38.7784 seconds during the two-hour session. That was a big improvement from his best time Friday, 1:40.0821, which placed him ninth overall.

SEE: Session 3 Test Results | Overall Test Results

Ilott’s time Saturday morning was the quickest overall in three sessions of testing leading into The Thermal Club $1 Million Challenge on Sunday at the 17-turn, 3.067-mile circuit near Palm Springs, California.

Reigning series champion Alex Palou, quickest in both sessions Friday, ended up second today at 1:38.8308 in the No. 10 DHL Chip Ganassi Racing Honda. Christian Lundgaard, second overall Friday, slipped to third in this session at 1:39.0659.

Scott McLaughlin was another big climber besides Ilott. McLaughlin ended up fourth with a top lap of 1:39.0716 in the No. 3 XPEL Team Penske Chevrolet after finishing Friday 16th at 1:40.3930.

Pato O’Ward rounded out the top five and showed consistent speed with his best lap of 1:39.1191 in the No. 5 Arrow McLaren Chevrolet. He was sixth overall Friday at 1:39.9124.

Drivers started coming to better grips with the technical circuit located at the private club at the base of the Santa Rosa Mountains during this session. The top 21 drivers on the overall time chart so far turned their best laps this morning under sunny skies and cooler temperatures.

Up next is the final session of the Open Test from 4-6 p.m. ET today. Then qualifying, which starts at 8 p.m., will divide the 27-driver field for two heat races Sunday. Peacock and the INDYCAR Radio Network will provide live coverage of both sessions.

Those 10-lap heat races Sunday will whittle the field to 12 drivers for the 20-lap Sprint for the Purse non-points special event, with the winner of that race claiming $500,000. The 20-lap dash for cash will be divided into two 10-lap segments.

Live coverage of the heat races and Sprint for the Purse starts at 12:30 p.m. ET Sunday on NBC, Peacock and the INDYCAR Radio Network.

This Open Test session was halted three times, once for repair to a track curb, once for Romain Grosjean going off track in Turn 15 in his No. 77 Juncos Hollinger Racing Chevrolet and once for Kyle Kirkwood’s spin into the barrier in Turn 8 in the No. 27 AutoNation Honda fielded by Andretti Global. Kirkwood tapped the rear wing of his car into the barrier but was unhurt.

“To be honest, I’ve been losing time to my teammates all the past day and a half, all through Turn 8,” Kirkwood said. “I haven’t been able to figure out why, so I was like, ‘This is the time to send it,’ to see if I could do any better. And all the sudden you can see the way the car reacts over that bump and just snapped on me.”