Johnson won at Hogan's Alley with a tournament record 21-under 259, sealing his victory with a pair of birdies in the short span of play in between two late weather delays Sunday.
When Johnson drained a 14-foot birdie putt at the 17th hole to take a two-stroke lead over Brian Davis, he had a wide smile on his face and emphatically pumped his fist. But the real celebration had to wait.
"As far as momentum and a big putt, that was a big one," said Johnson, the 2007 Masters champion. "I didn't have a number in my head, but I figure if you get to 21, you have got a pretty good chance."
Johnson's closing 6-under 64 left him three strokes ahead of Davis, who had a closing 68.
"Zach won the tournament, I didn't lose it," Davis said. "It was a weird feeling walking up 18 knowing you can't win."
When the horn sounded to suspend play the first time, Johnson was approaching his tee shot at No. 15 that had landed in the right rough short of a bunker. After that delay, he hit his approach onto the green and made the putt to get back to 20 under.
By time play was stopped again 31 minutes later, before he teed off at 18 for a closing par, Johnson was ready for the plaid jacket.
"Quite frankly, the biggest one, I thought, was probably on 15," he said. "It calmed me down."
The delays were because of threatening weather. Light rain fell despite sunny skies after the second delay lasted 46 minutes, a minute shorter than the first one.
Jeff Overton and Ben Crane both shot 67 to finish tied for third at 17 under. Scott Verplank (65) and Bryce Molder (70), who led after the second and third rounds, were another shot back.
Davis was again contending for his first PGA Tour victory, six weeks after the 35-year-old Englishman called a two-stroke penalty on himself on the first hole of a playoff at Hilton Head.
At Colonial, Davis was 19 under with a two-stroke lead after a 5 1/2-foot putt at the seventh hole. But that was his last birdie of the day. A 9-footer at No. 17 slid just past the cup, then he finished with a bogey.
It is the seventh PGA Tour victory for Johnson and first since winning in San Antonio last May. His best finish through 12 tournaments this season had been a tie for 12th at the Sony Open in Hawaii the second week of the season.
Along with the plaid jacket, Johnson got a $1.116 million check.
"Going into the back nine, my mindframe was I don't care if I win this, I don't care if I lose it, I'm content with whatever happens," he said. "I'm going to go out fighting, I'm going to go out aggressive."
Johnson's clinching shot at the 381-yard 17th was his fifth birdie on the back nine, though he gave back one of those with his only bogey over his last 2 1/2 rounds.
Three of those birdies came on putts of at least 22 feet in a four-hole stretch. He took the lead for good when he drained the longest of the three, a 25-footer at the 427-yard 15th hole soon after the initial weather delay.
Kenny Perry was 19 under in both of his Colonial victories, in 2003 and 2005. The next-lowest score before this week was 17 under by a trio of players last year when Steve Stricker won on the second playoff hole.
The Colonial score was the lowest on the PGA Tour for a four-round tournament since Geoff Ogilvy won the season-opening SBS Championship in Hawaii at 22-under 270.
At Hilton Head in April, Davis made a birdie on the 72nd hole to get into a playoff with Jim Furyk. Davis ticked a loose reed in a hazard during a backswing in the playoff and immediately called over a rules official to point out something that might have otherwise gone unnoticed. A television replay confirmed the violation.
Davis tied for 57th at New Orleans and missed the cut his last three tournaments before getting to Colonial.
"If you would have said at the start of the week after three missed cuts you are going to finish second, you would be delighted," he said. "Obviously, I had a chance today, I couldn't quite get over the hump."
Molder led alone halfway through the tournament and shared the lead with Davis at the start of the final round, but his final birdie Sunday came on the 10th hole, the same as Saturday, when he finished with eight consecutive pars instead of being able to lower his score.
This time, he had bogeys at Nos. 16 and 17.
"You certainly learn," said the four-time All-American from Georgia Tech who is still looking for his first PGA Tour victory nine years after turning pro. "This is the closest I've been to winning. ... Zach put the pedal down and he really kept going. That's what you have to be able to do."
DIVOTS: Johnson and Phil Mickelson are the only players who have PGA Tour wins in each of the last four seasons (2007-10). ... Mickelson missed the cut at Colonial at 4 over when he could have been the No. 1 player in the world with a victory. ... Ian Poulter, the No. 6 player in the world, shot 76 Sunday in the first group off. His 7-over total was the worst among the 76 players who made the cut. ... Stricker finished at 8 under, tied for 38th, in his first event after a six-week hiatus because of a chest injury.
