Dustin Johnson rallies at Firestone for 2nd straight win

Jason Day, from Australia, tees off on the third hole during the final round of the Bridgestone Invitational golf tournament at Firestone Country Club, Sunday, July 3, 2016, in Akron, Ohio. (AP Photo/Tony Dejak) (The Associated Press)

Jason Day, from Australia, watches his eagle shot on the second hole during the final round of the Bridgestone Invitational golf tournament at Firestone Country Club, Sunday, July 3, 2016, in Akron, Ohio. (AP Photo/Tony Dejak) (The Associated Press)

Dustin Johnson watches his missed birdie putt on the first hole during the final round of the Bridgestone Invitational golf tournament at Firestone Country Club, Sunday, July 3, 2016, in Akron, Ohio. (AP Photo/Tony Dejak) (The Associated Press)

In his first start since winning the U.S. Open, Dustin Johnson won another World Golf Championship on Sunday.

Johnson ran off three birdies on the back nine at Firestone and closed with a 4-under 66 to win the Bridgestone Invitational. He was helped in part by a surprising collapse by Jason Day.

Day, the world's No. 1 player, was tied for the lead when he hooked a 3-wood off the tee on the par-5 16th, hit across the fairway and tried to bend a shot around the pond. He went into the water, making double bogey.

Day did not hit a green in regulation over his last six holes.

Johnson now has three WGC titles, and goes to the British Open as the player to beat.