Last year's race winner at Sonoma, Penske's Will Power, was comfortably back in charge on the 12-turn, 2.31-mile permanent road course with a late flying lap of 1:18.6887s (109.114mph) putting him on top of the timesheets after the sole Friday practice session.

"This is definitely a Penske track," lamented Andretti Autosport's Ryan Hunter-Reay, recalling last year's historic 1-2-3 lock-out by the Penske squad. Power agreed that a good starting position could once again prove decisive on race day.

"It will be very important to start up front in the race if you want to finish on the podium - I like the new layout of the track and the track was fast for the first day," said Power. "We'll look at our notes and try to go faster tomorrow. We'd really like a pole position to keep moving forward in the Championship race and we'll see if we can do that tomorrow

Sure enough, Power's team mate Ryan Briscoe was 0.1895s, narrowly ahead of Simon Pagenaud who recorded the third fastest time of the day just in front of Dario Franchitti. Also having good days at the office were road course specialists Rubens Barrichello and Sebastien Bourdais, both of whom set faster best laps than Scott Dixon and Graham Rahal.

Returning to duty after missing the race at Mid-Ohio with a hand injury, Charlie Kimball had limited track time and completed only five laps, after running off the track and hitting the wall at turn 3 early in the session to bring out the first of the session's two red flags.

"It's obviously disappointing to start off practice like that," admitted Kimball. "I overestimated the track grip a little bit and spun off and we weren't able to get back out today. Our teammates are quick so we should be in good shape for tomorrows practice and more importantly tomorrows qualifying."

The other stoppage was for a brief and less serious off for Josef Newgarden at turn 7 near the end of the session. Graham Rahal and Mike Conway received a drive-thru penalty during the session for a pit lane entry violation.

Sebastian Saavedra impressed on his first IndyCar outing since the Indianapolis 500, setting the tenth fastest time in the AFS Racing/Andretti Autosport co-entry which was still within a second of Power's benchmark.

"It was great out there today, I'm very excited to be back in the IndyCar," he said. "It's very different from what I remember from last year. It's been good so far. We've managed to consistently improve the car together with my teammates', and we just need to keep fighting. The front guys are pretty quick and we need to close that gap."

Katherine Legge was 26th fastest, and was 2.4989s off the top time on her return to a road course for Dragon Racing for the first time since Sao Paulo.

All 27 drivers got the chance to take part for the entire 75 minute afternoon session on Friday, rather than the usual split session reserving a portion of the running for rookies and those outside the top ten in the IZOD IndyCar Series championship standings. That's because of the changes made to the circuit in the last month designed to improve overtaking action.

Full Friday practice session times available.