His No.17 Roush Racing Ford was 0.592 seconds faster to the checkered flag than runner-up Kyle Busch, who was the race's pole sitter.
The victory was Kenseth's fourth of the season and 14th of his Nextel Cup career.
"I didn't think we had quite the car today honestly, I thought Jeff Burton had everybody covered, but once we got to the lead clean air helped my car," Kenseth said after also winning the Busch Series race on Friday night.
In the points race, Johnson held on to first place with 3,365. Kenseth is second with 3,307, and Kevin Harvick is third with 3,048.