The race at the Richmond International Raceway was postponed from Saturday because of the threat of tropical storm Hanna.
The two-time defending NASCAR Sprint Cup Series champion won the race by holding off a furious challenge from Tony Stewart in the final laps.
Having also won last Sunday's Pepsi 500 at Fontana, Calif., Johnson has now won his last two Sprint races and 37 in his Sprint Cup career.
"It's hard not to feel that way," Johnson told The Charlotte (N.C.) Observer when asked if he felt like his team is peaking at the right time. "I think our chances are good."
Denny Hamlin, Dale Earnhardt Jr. and Mark Martin finished third through fifth, giving Chevrolet a top-five sweep at Richmond.
Clint Bowyer finished 12th, clinching the 12th and final spot in the "Chase for the Sprint Cup" championship beginning next Sunday.