Haas shot a 7-under 64 at TPC Scottsdale to take a two-stroke lead. The birdie on 16 capped a five-hole stretch he played in 5 under, with birdies on Nos. 12 and 13 and a 20-footer for eagle on the par-5 15th.
"Once you get a cushion like that, you can free your swing up a little bit," Haas said.
The 16th, playing 151 yards to a front pin, tripped up Rickie Fowler and Justin Thomas. Fowler bogeyed it in a 66 that left him tied with Billy Horschel, Bryson DeChambeau, Chris Kirk and Chesson Hadley. Thomas made a double bogey in a 68.
Fowler hit short into the right bunker and two-putted from 30 feet. The fans let him hear it, too — at 9:30 a.m. with only the general-admission sections full.
"I may be somewhat of a fan favorite, but they weren't holding back," Fowler said. "I was a little disappointed in some of the stuff that was said."
Coming off three straight birdies to tie for the lead, Thomas hit a wedge in the front left bunker, blasted across the green and three-putted from the fringe.
"I just barely caught it heavy, but I thought it was at least going to cover the front, and there was just no sand in the bunker," Thomas said.
He bogeyed the par-4 17th after chipping into the water, and then was angered when a woman screamed while Jordan Spieth was teeing off on 18.
"That girl just yelled right in Jordan's downswing," Thomas said. "There's just no place for that. You saw it with Tiger (Woods) last week. I get it, late in the day, at a place like Phoenix, I'm sure they're a couple in."
Spieth hit a 325-yard drive into the fairway and finished with a par for a 72.
While Fowler lost a stroke on 16, he had an eagle and two birdies on the other three holes in the chaotic closing stretch.
"Some good and bad all around," Fowler said.
Fowler eagled the 15th, hitting a 5-wood 232 yards to 2 feet. He drove the green and two-putted for birdie on the 17th and holed a 30-foot chip on the par-4 18th. On his second nine, he made a 43-foot birdie putt on the par-3 fourth and a 14-footer on the par-4 eighth.
Haas also finished on the front nine, making birdies on Nos. 2 and 4.
"I kind of hit a bad putt on 2, but it hit the back of the cup and went in," Haas said. "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. Hopefully, it will be one of those weeks."
Haas won the first and the last of his six PGA Tour titles in the desert, taking the La Quinta event in California in 2010 and 2015.
"I like playing in the desert," Haas said. "I love the turf. I love the grass."
Fowler wore a pin on his hat with a picture of Griffin Connell, the area boy who died Jan. 23 at age 7. Connell was born with a rare airway disorder.
"Just kind of humbles you, grounds you a bit, and makes you realize that there's a lot bigger things than just playing golf," Fowler said.
Former Arizona State star Jon Rahm was at 67 in a group that included Bubba Watson.
The winner two weeks ago in La Quinta, Rahm eagled the par-5 third on his second nine.
"I don't think I missed a single shot after that eagle," Rahm said.
Playing directly behind Fowler's group, Rahm and fellow former Arizona State player Phil Mickelson each birdied the 16th for the loudest roars on the hole in the morning — other than the helicopter that buzzed the stands just before playing partner Xander Schauffele hit.
Mickelson got a good bounce to set up a 5-footer, with the fans chanting "Phil! Phil!"
"He's Phil, he can actually argue he tried to do that," Rahm said.
Wearing a "Rahmbo" headband, Rahm made a 12-footer .
The 47-year-old Mickelson had a 70 in his record-tying 29th start in the tournament he won in 1996, 2005 and 2013. Mickelson's brother, Tim, coached Rahm at Arizona State and was his agent. Tim Mickelson is now his older brother's caddie.
Hideki Matsuyama, a playoff winner over Fowler in 2016 and Webb Simpson last year, had a 69 playing alongside his two sudden-death opponents. The Japanese star is trying to match Arnold Palmer's record of three straight victories. Palmer accomplished the feat from 1961-63.
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