FT. Worth, Texas, May 24, 2012 (AFP) - "A fantastic way to start," Dufner said. "You have some questions after a win last week, how are you going to respond to that? I came out really quick today and got some birdies."
Former winner Johnson grabbed the first-round lead with a six-under 64.
"Today was great," Johnson said of his 13th consecutive round in the 60s at this event.
"I got off to a good start. I just hit quality shots. I didn't put myself ever in a position that was too worrisome.
"The times when I was maybe just in the rough and I had to get myself up and down, I managed to do that.
"I gave myself a lot of opportunities. I made some long putts, but I missed some shorter ones, so it probably evened out in the end."
Dufner won his first PGA title on April 29 at New Orleans, got married the next weekend and joined Hunter Mahan as 2012's only repeat winners by taking the title last week at the Byron Nelson Championship in nearby Irving.
Dufner was in a group at five-under along with fellow Americans Harris English, Tom Gillis and Kyle Reifers.
He birdied five of his first eight holes at Colonial Country Club. He tossed in two more birdies and two bogeys for his share of second.
Dufner began his tournament with a round in the 60s for the eighth time in 14 starts this year.
Spain's Sergio Garcia and Argentina's Andres Romero were in a group at four-under 66, just two shots back of the leader.
Garcia, seeking his first US tour win in four years, had an eagle at the par-five first -- his 10th hole of the day.
Garcia won this event in 2001 -- the first of his seven US tour titles -- and Johnson won two years ago for his most recent PGA Tour victory.
American Rickie Fowler opened with a two-under 68. Fowler has a victory and a tie for second in his last two tournaments.
Matt Kuchar, winner of The Players Championship two weeks ago, carded a 72.
Leading scores on Thursday after the first round of the $6.4 million PGA Tour Crowne Plaza Invitational golf tournament (USA unless noted, par-70):
64 - Zach Johnson
65 - Harris English, Tom Gillis, Jason Dufner, Kyle Reifers
66 - Chris DiMarco, Tommy Gainey, Sergio Garcia (ESP), Andres Romero (ARG)
67 - Ryan Moore, Daniel Summerhays, Roberto Castro, Brendon de Jonge (ZIM), Brandt Jobe
68 - Charlie Wi (KOR), Ken Duke, Ryan Palmer, Rickie Fowler, Martin Flores
69 - Chris Stroud, Blake Adams, Jim Furyk, Greg Owen (GBR), Pat Perez, John Senden (AUS), Hunter Mahan, Charley Hoffman, Bo Van Pelt, Justin Leonard, Michael Thompson