Rahal leads RLL 1-2 from Sato on day one of IndyCar Phoenix test

The test was the squad's first on a short oval with the 2018 aerokit-equipped car, but Rahal and Sato were the only drivers to top 189mph lap averages, lapping the 1.022-mile course in 19.4574s and 19.4600s respectively.

"We're good and Takuma is right behind us," Rahal said afterward.

"And frankly, that lap wasn't anywhere near what the potential was. We were on a [19.30-second lap], but I caught traffic.

"Both cars have pace, and so that's awesome.

"We're used to coming here and getting our butts kicked. To be able to come here and be competitive with this aerokit is awesome."

Sato, who had topped the day's earlier afternoon session with a 186mph lap, added: "I was happy to get back behind the wheel.

"This is our first oval test with the team. It wasn't flawless because we had some electrical issues again, but the engineers deal with it very well.

"Once we get going, I think we were very comfortable."

Rahal and Sato beat the Team Penske-Chevrolets of Simon Pagenaud and Josef Newgarden, who were third and fourth, while Tony Kanaan continued the AJ Foyt Racing Chevrolet team's strong pre-season form with fifth.

Kanaan's team-mate Matheus Leist, who topped Thursday's rookie session, had the only notable incident of the session with a quick spin when he came off the throttle too abruptly as Kanaan pulled out of the pitlane.

He nonetheless finished 10th and top of the rookie runners.

Three of the Andretti Autosport-Hondas made the top 10, with Ryan Hunter-Reay, Marco Andretti and Alexander Rossi in sixth, seventh and ninth respectively.

Four-time IndyCar champion Scott Dixon, who tested the aeroscreen cockpit protection device a day earlier, was eighth for Chip Ganassi Racing.

Will Power was 11th in the third Penske ahead of the quicker of the two Dale Coyne Racing-Hondas, driven by Sebastien Bourdais, although his best effort of the day was from the afternoon session.

James Hinchcliffe encountered electrical troubles during the day that kept him off track for a long period, although he was able to record the 17th fastest time in the second SPM car, with Robert Wickens 14th.

Carlin pair Charlie Kimball and Max Chilton had propped up the times in the earlier afternoon session, but picked up speed in the evening to end up 15th and 18th respectively and completing 39 and 78 laps.

Gabby Chaves' Harding Racing-Chevrolet was last, but less than 0.9 seconds from Rahal's pacesetting lap.

Evening session times