Will Power beat Penske team-mate Juan Pablo Montoya to the fastest time of a shortened first day of IndyCar testing at Barber Motorsports Park on Monday.
The Australian, a three-time runner-up in the series, posted a best time of 1m07.6492s to emerge on top in a session that was cut to half of the scheduled seven hours of work because of poor visibility in the morning.
Power led a Penske 1-2-3 on the opening day, with Montoya an impressive second as he continues his preparations for his return to single-seater racing.
The Colombian was less than a tenth off Power's pace, with Helio Castroneves completing Penske's domination in third position.
"I'm trying to learn how to get more out of the car and we're getting there," said Montoya at the end of the day.
"It was good today, but there's a couple of places that I need to do a little better job and be a little cleaner, but we're getting there."
Reigning champion Scott Dixon was the quickest non-Penske driver in fourth for Ganassi, while AJ Foyt Racing's Takuma Sato rounded up the top five in the fastest Honda-powered car.
Ryan Briscoe was sixth quickest in the second Ganassi car, ahead of Justin Wilson, Simon Pagenaud, James Hinchcliffe and Ryan Hunter-Reay, who completed the top 10.
The day had three stoppages caused by Mikhail Aleshin, Graham Rahal and Sebastien Bourdais, who crashed at Turn 6, the Frenchman finishing at the bottom of the times.
The test finishes on Tuesday.
Pos Driver Team/Engine Time Gap Laps 1. Will Power Penske/Chevy 1m07.6492s 48 2. Juan Pablo Montoya Penske/Chevy 1m07.7170s +0.0678s 55 3. Helio Castroneves Penske/Chevy 1m07.7214s +0.0722s 51 4. Scott Dixon Ganassi/Chevy 1m07.8225s +0.1733s 40 5. Takuma Sato Foyt/Honda 1m07.8619s +0.2127s 39 6. Ryan Briscoe Ganassi/Chevy 1m07.8834s +0.2342s 44 7. Justin Wilson Coyne/Honda 1m07.8863s +0.2371s 31 8. Simon Pagenaud Schmidt/Honda 1m08.0682s +0.4190s 35 9. James Hinchcliffe Andretti/Honda 1m08.1629s +0.5137s 32 10. Ryan Hunter-Reay Andretti/Honda 1m08.3194s +0.6702s 30 11. Charlie Kimball Ganassi/Chevy 1m08.3209s +0.6717s 41 12. Tony Kanaan Ganassi/Chevy 1m08.3254s +0.6762s 42 13. Mike Conway Carpenter/Chevy 1m08.4734s +0.8242s 42 14. Graham Rahal Rahal/Honda 1m08.4907s +0.8415s 37 15. Josef Newgarden Fisher/Honda 1m08.5798s +0.9306s 25 16. Sebastian Saavedra KV/Chevy 1m08.6539s +1.0047s 50 17. Marco Andretti Andretti/Honda 1m08.6688s +1.0196s 28 18. Mikhail Aleshin Schmidt/Honda 1m08.7296s +1.0804s 28 19. Jack Hawksworth Herta/Honda 1m08.9223s +1.2731s 36 20. Carlos Munoz Andretti/Honda 1m08.9299s +1.2807s 42 21. Oriol Servia Rahal/Honda 1m09.2164s +1.5672s 7 22. Sebastien Bourdais KV/Chevy 1m09.6668s +2.0176s 11