Power, who scored his 24th career IndyCar win but just his third on an oval, increased his points lead from four to 39 over Helio Castroneves, his Team Penske teammate, at Milwaukee.
The 33-year-old Australian started on the pole and put on a dominating performance at Milwaukee, leading 229 of 250 laps. Castroneves was never a factor in that race, as he started eighth and finished 11th.
Power won last year's races at Sonoma and Fontana, which gives him a lot of confidence heading into the final two events this season.
"The win at Milwaukee last weekend was very gratifying, almost as much as my win at Auto Club Speedway last year," Power said. "I really had a lot of confidence coming into the year about Milwaukee, so it's nice that we were able to realize our potential there.
"Certainly, we are in a good position going into the last two weeks of the season. We have a lot of confidence in our ability as a team at Sonoma and Auto Club Speedway, but there is still over 150 points on the table, with Fontana being a double-points race. Our path is easier now, but it's by no means easy."
Power is the only driver with multiple IndyCar victories at Sonoma. He won back-to-back races at this track from 2010-11 and then scored his third victory here one year ago. Power finished second at Sonoma in 2012.
"Sonoma is just a very technical racetrack," he said. It's a place where you have to really hit your marks and be precise. For whatever reason, that fits my driving style perfectly.
"After the test at Sonoma a couple of weeks ago, it seems like we'll have another fast one this weekend. We're going for wins. That's what got us here, and that's what will keep us in the points lead."
Castroneves is a three-time Indianapolis 500 winner but has yet to win an IndyCar championship. He remains positive that it can happen this year.
"You just have to put last weekend out of your mind, knowing that you are probably going to lose even more points at Sonoma if you hang on too long to what happened in Milwaukee," Castroneves said. "Will did exactly what he needed to do last weekend. Now we need to come out and have that same kind of maximum-points weekend either this weekend or next weekend at Auto Club Speedway."
Castroneves has one victory at Sonoma (2008). He finished seventh here last year.
Series: Verizon IndyCar. Date: Sunday, Aug. 24. Race: GoPro Grand Prix of Sonoma. Site: Sonoma Raceway. Track: 2.385-mile, 12-turn road course. Start Time: 4:40 p.m. ET (expected green flag). Laps: 85. Miles: 202.73. 2013 Winner: Will Power. Television: NBC Sports Network. Radio: IMS Radio Network/SIRIUS XM Satellite.