DORAL, Fla. - A month after he returned from his curious leave of absence, Dustin Johnson was posing with another big trophy.

In a power show Sunday on the Blue Monster, Johnson was flawless on the back nine and blasted two big drives to finish off a 3-under 69 and win the Cadillac Championship for his second World Golf Championship title.

Johnson took advantage of a collapse by J.B. Holmes, who lost a five-shot lead and closed with a 75 to finish one shot behind. Masters champion Bubba Watson opened with four birdies in seven holes to lead by two shots, only to make three bogeys in a four-hole stretch on the back nine. He shot 71 and finished two behind.

Johnson won for the ninth time in his PGA Tour career and moved to No. 6 in the world.

It looked as though the 30-year-old Johnson was never gone.

He returned just five weeks ago from a six-month leave of absence to seek professional help for what he described only as personal challenge. Golf.com reported in August that Johnson had failed a cocaine test for the second time, and that he previously was suspended in 2012 under similar circumstances.

Johnson only said, "No," when asked if he failed a drug test in an interview before his return.

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The swagger was back at Trump National Doral, especially on the finishing holes. But when he tapped in for par, it was clear this victory meant more than the others. He walked off with fiancee Paulina Gretzky -- the daughter of hockey great Wayne Gretzky -- and their son, Tatum, who was born in January.

"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. ... It's tough. I'm so excited right now, I can't hardly talk. It feels great. The one definitely, by far, is the best one."

One day after Johnson made a hole-in-one on the par-3 fourth hole, he nearly did it again, missing the cup by an inch. That was his first birdie, and two birdies on the par 5s around the turn drew him closer as Watson began to slip.

Watson laid up into the rough on the par-5 12th hole, caught a plugged lie in a bunker and made his second straight bogey to create a three-way tie for the lead with three of the longest hitters in golf. Johnson took the lead for the first time when he made a 10-foot par putt on the 14th hole, and Holmes missed his par from 6 feet.

The pivotal moment came on the par-3 15th, when Johnson rolled in a birdie from just inside 15 feet for a two-shot lead.

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He made all the right moves the rest of the way.

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, forcing him to miss the Ryder Cup and the FedEx Cup playoffs.

And now he's back.

In five tournaments, he has missed the cut twice, lost in a playoff at Riviera and tied for fourth at Pebble Beach.

It was the second close call this year for Holmes, who lost in a playoff at Torrey Pines. It was a struggle from the start, and Holmes lost his five-shot lead in the first 30 minutes, and fell behind with three bogeys in his opening six holes.

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His lone birdie was a two-putt on the 293-yard 16th hole, but he didn't have good birdie chances on the final two holes. And Johnson didn't make any mistakes. He twice hit tee shots over 300 yards on the two closing holes, the last hole so bold that it challenged the corner of the water. It sailed right over, and Johnson was on his way.

Watson went bunker-to-bunker on the 11th for bogey, made another on the 12th and drove into the trees on the 14th for another bogey.

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.