Alex Palou set the pace in the second test session at The Thermal Club to complete a clean sweep in Palm Springs.
Felix Rosenqvist set the second-best time for Meyer Shank Racing, with former Formula 1 driver Romain Grosjean in third.
The second test session at The Thermal Club for three hours of running ahead of the $1 Million Challenge.
Pietro Fittipaldi set the pace in the opening minutes with a 1:42.7896 ahead of Juncos Hollinger Racing’s Grosjean.
Santino Ferrucci usurped the Brazilian’s effort to go fastest with 10 minutes on the clock as the sun shone over the circuit.
The A. J. Foyt Racing driver continued to hold the fastest time 20 minutes into the session, while Colton Herta suffered a difficult front end on his Andretti.
The benchmark was lowered as Callum Ilott, with a 1:42.3147, topped the timesheets on his second lap.
Former Formula 1 driver Marcus Ericsson became the first to break the 1:42 barrier, setting a 1:41.7540 to go fastest before being beaten by Tom Blomqvist.
40 minutes into the session, New Zealander Scott McLaughlin improved to set the quickest time ahead of Rosenqvist and Grosjean, who returned to the top three.
The red flags were soon brought out as Christian Rasmussen stopped on the circuit, causing the first stoppage of the day.
The session resumed with just over two hours remaining, and a flurry of cars joined the circuit in Palm Springs.
With a 1:40.5823, McLaughlin remained the fastest driver an hour into the session as the 27-car field familiarised themselves with The Thermal Club.
After a brief lull, Will Power bested his Team Penske teammate’s effort as the times continued to tumble.
Argentinian Agustin Canapino took fourth place, completing 10 laps almost halfway through the session, while Alex Palou sat in P5.
After a quiet session, Colton Herta broke into the top three, slotting into second place for Andretti with a 1:40.5748, with one hour and 18 minutes remaining.
After just two laps in the session, 22-year-old Christian Lundgaard went quickest with a 1:40.2914, two-tenths quicker than his nearest rival, Power.
Scott Dixon finally ventured onto the circuit with an hour remaining and began setting consecutive lap times in his number nine Chip Ganassi Racing car.
Rinus VeeKay set a new benchmark at 1:40.2255, just over half an hour to go, ahead of Lundgaard and Power.
Grosjean completed 22 laps with half an hour remaining and set the best time ahead of the Dutchman as the three-hour session drew to a close.
Rosenqvist briefly jumped to the top of the standings before the reigning champion Palou laid down a marker, setting a 1:39.3373 with 10 minutes left, going quickest.
Palou remained the pacesetter and topped both sessions on Friday, in a peerless start to the weekend at The Thermal Club.
