"The putter was hot the first nine holes," Haas, a six-times PGA Tour winner, told reporters after a round that included a 30-foot birdie at the second hole, his 11th.
"I kind of hit a bad putt but it hit the back of the cup and went in," he said.
"So one of those days where I could have easily three-putted that if it had run by, but it went in and saved two shots there basically."
After starting the season with two missed cuts followed by a tie for 54th, Haas was not getting too carried away by his good start.
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"This is only one round," he said. "I'm not saying I'm cured (of recent putting woes) by any means."
Fowler joined a group of four fellow Americans at five-under 66, with his lone bogey coming at the par-three 16th hole, which is famous for its rowdy fans who eschew usual golf etiquette by routinely booing bad shots.
But Fowler thought they went too far.
"I may be somewhat of a fan favourite, but they weren't holding back," he said."I was a little disappointed in some of the stuff that was said and I don't want much negativity -- the normal boos for missing a green, that's fine, but leave the heckling to a minimum and make it fun."
Thomas also heard from the gallery when he ran up a double-bogey at the 16th, and he also made a mess of the par-four 17th, where he pitched his second shot from 50 yards over the green into a water hazard on his way to a bogey.
"Two birdie holes and to play those three-over today is definitely disappointing, but the fact that I did that and I'm still more than right there in a great position is definitely a positive note that I can leave today with," he said after shooting a 68.
Thomas was also upset by the crowd, particularly a scream from a spectator during Jordan Spieth's tee shot at the last.
"That girl just yelled right in Jordan's down swing," Thomas said. "I was so upset. It doesn't matter who it is, whether it's me or Jordan or anybody else in the field, I mean there's just no place for that."
(Reporting by Andrew Both in Adelaide, South Australia; Editing by Greg Stutchbury)
