Ryan Hunter-Reay set the pace in the opening practice session for this weekend's IndyCar race at Sonoma.
The Andretti driver produced his 1m17.7150s effort with 13 minutes still remaining on the clock and his time held until the chequered flag.
His lap was just 0.2 seconds slower than Dario Franchitti's pole time last year and gave engine supplier Honda an early boost on a weekend where rival Chevrolet was confirmed as manufacturers' champion.
Reigning champion Scott Dixon came closest to matching Hunter-Reay; the Ganassi driver finishing up 0.184s down on Hunter-Reay's time, with team-mate Tony Kanaan an additional 0.1s behind in third.
Penske duo Will Power and Helio Castroneves left it late to join the on-track action and both rebounded from brief trips over the grass to round out the top five.
James Hinchcliffe, Simon Pagenaud and Mike Conway also went off the track over the course of the morning, although the session was completed under greens.
Pos Driver Team/Engine Time Gap Laps
1. Ryan Hunter-Reay Andretti/Honda 1m17.7150s 8
2. Scott Dixon Ganassi/Chevy 1m17.8990s +0.1840s 8
3. Tony Kanaan Ganassi/Chevy 1m18.1895s +0.4745s 10
4. Helio Castroneves Penske/Chevy 1m18.2732s +0.5582s 9
5. Will Power Penske/Chevy 1m18.4046s +0.6896s 9
6. Ryan Briscoe Ganassi/Chevy 1m18.4063s +0.6913s 14
7. James Hinchcliffe Andretti/Honda 1m18.5220s +0.8070s 15
8. Josef Newgarden Fisher/Honda 1m18.5416s +0.8266s 15
9. Sebastien Bourdais KV/Chevy 1m18.5498s +0.8348s 10
10. Marco Andretti Andretti/Honda 1m18.5748s +0.8598s 11
11. Charlie Kimball Ganassi/Chevy 1m18.7281s +1.0131s 15
12. Juan Pablo Montoya Penske/Chevy 1m18.7962s +1.0812s 10
13. Takuma Sato Foyt/Honda 1m18.8442s +1.1292s 11
14. Carlos Munoz Andretti/Honda 1m18.8563s +1.1413s 9
15. Justin Wilson Coyne/Honda 1m18.9591s +1.2441s 12
16. Simon Pagenaud Schmidt/Honda 1m18.9928s +1.2778s 13
17. Graham Rahal Rahal/Honda 1m18.9988s +1.2838s 15
18. Mikhail Aleshin Schmidt/Honda 1m19.2681s +1.5531s 14
19. Sebastian Saavedra KV/Chevy 1m19.3563s +1.6413s 17
20. Mike Conway Carpenter/Chevy 1m19.3627s +1.6477s 18
21. Jack Hawksworth Herta/Honda 1m19.7091s +1.9941s 16
22. Carlos Huertas Coyne/Honda 1m19.9732s +2.2582s 18
All drivers use Dallara chassis