Johnson finished 4.4 seconds ahead of Hendrick Motorsports teammate Dale Earnhardt Jr. after leading for 255 of 334 laps at the AAA Texas 500.
It was his sixth win of the season and the 66th of his Sprint Cup Series career.
More importantly, Johnson forged a seven-point lead over Matt Kenseth in the championship standings with just two races remaining.
Kenseth, who came into Sunday in dead heat with Johnson, shook off a pit road penalty to claim a fourth-place finish.
Third place went to Joey Logano while Kasey Kahne claimed fifth.