Johnson made up a five-shot deficit on J.B. Holmes and had a one-shot lead as he stood on the 18th tee at Trump National Doral, among the most daunting shots in golf. He produced his best drive all week, a monster shot that cleared the corner of the water and sent him to a routine par and a victory that never felt better.
He left the green holding his 7-week-old son, Tatum, with fiancee Paulina Gretzky at his side.
"I knew I was really good," Johnson said. "I knew there was something I was missing that could make me great. I was working hard on that, and I think it's showing right now. I'm so excited right now, I can't hardly talk. It feels great. This one definitely, by far, is the best one."
Johnson holed two big par putts from 20 feet and 10 feet that put him in the lead on a back nine of survival, seized control with a 15-foot birdie putt on the 15th hole and powered home to a 3-under 69 and a one-shot victory over Holmes.
It was his ninth career win, and second World Golf Championship title, and it returned him to the elite in golf at No. 7 in the world.
Still lingering are questions about his curious six-month leave he announced in August that caused him to miss the final major and the Ryder Cup. He said it was to seek professional help for "personal challenges." Golf.com reported he had failed a second cocaine test, the first one in 2012 when he missed the Masters for what he called a back injury from lifting a jet ski from the water.
Johnson said again he has never failed a drug test. He said he was done talking about it in an interview with The Associated Press in January, and when pressed anew about why he had not been more forthcoming with answers, Johnson replied, "Because it's personal and frankly, it's not really anybody's business."
In an interview before he returned, Johnson said he was handling stress through too much partying. He said he spent time with his future father-in-law -- hockey great Wayne Gretzky -- and a person he described as a life coach.
There are no questions about his golf. The swagger was back, especially as he closed in on a victory.
Johnson won in his fifth start back -- Johnson lost in a playoff at Riviera and tied for fourth at Pebble Beach -- and did what few others could manage at Doral. He never made worse than a bogey all week, and he didn't have a single three-putt.
"If he's won nine times out here, you're pretty good," Holmes said after making only one birdie in a round of 75.
Holmes lost his five-shot lead quickly, thanks to three bogeys in his opening five holes, and Masters champion Bubba Watson opening with four birdies in seven holes. Watson went from a five-shot deficit to a two-shot lead on the front nine, but three bogeys in a four-hole stretch on the back nine -- two from bunkers, one from the palm trees -- ended his big run. He closed with a 71 and finished two shots behind.
"A couple of shots, just missed the fairway by a few feet. Missed the green by a few feet. That's what this golf course does," Watson said. "If you're just off, it can get to you real fast."
Holmes made his lone birdie with a 3-wood onto the green at the 293-yard 16th hole for a two-putt birdie that pulled him to within one shot. With no margin for error, Johnson was at his best over the closing two holes, especially the 18th with Holmes already in the fairway.
"I absolutely smashed it," Johnson said. "I wasn't worried about it getting over the lake. ... I played the hole the best I've played it all week. And it was a good time to do that."
Adam Scott (71) and Henrik Stenson (72) tied for fourth, though they were five shots behind.
Rory McIlroy got his 3-iron back, the one he heaved into the water on the eighth hole Friday. A diver retrieved and Donald Trump delivered it to him on the range. McIlroy used it on the 18th hole and hit into the water for a double bogey and a 72. The world's No. 1 player, who missed the cut in the Honda Classic last week, tied for ninth.
Johnson finished at 9-under 279, adding to the WGC title he won in Shanghai at the end of 2013. He was on top of his game, one of golf's most athletic figures who already had contended in three majors. Then came the indefinite leave. And now he's back.
"I've been working hard on my game and been working hard on me," Johnson said. "And so it means a great deal to have success right out of the gate. It gives me a lot of confidence, too."
Johnson Rallies For First Win Since Return
Dustin Johnson shot a 3-under 69 on Sunday to beat J.B. Holmes by one stroke at the WGC-Cadillac Championship on the Blue Monster at Doral.
Johnson On Big Comeback At Doral
Bob Harig speaks with Dustin Johnson about overcoming a five-shot deficit to win the WGC-Cadillac Championship and how his time away from the game has made a positive impact on his life.
Holmes Comes Up 1 Shot Short At Doral
The putter wasn't working for J.B. Holmes in the final round at the WGC-Cadillac Championship.
Watson Grinds Way To Third-Place Finish
World No. 2 Bubba Watson discussed how hard it was for him this week at the WGC-Cadillac Championship.