Power turned a lap in 1 minute, 17.4126 seconds on the winding course at the base of wine country. He'll start in front Sunday when he attempts to win the race for the fourth time in five years.
The Australian broke his own track record in the first qualifying heat, finishing in 1:17.2393.
Josef Newgarden finished second, with Scott Dixon third and James Hinchcliffe fourth. Helio Castroneves, who trails teammate Power by 39 points in the overall race, finished sixth.
Qualifying is particularly important at Sonoma. No driver starting outside the top five has won the race since IndyCar arrived at the track in 2005.
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