Fowler and DeChambeau both carded five-under 66s at TPC Scottsdale for 10-under-par 132 totals, one stroke clear of compatriots Daniel Berger and Chez Reavie.
It's going to be a great weekend as there are 18 players sitting within three shots of the leaders, including Lefty Mickelson and world number 3 Jon Rahm, both at -7.
The WD is a bit of a surprise as there hasn't been much chatter about the defending champion dealing with any sort of injury, although Matsuyama's wrist and thumb were taped up during Round 1 when he shot a 69.
Matsuyama won the last two years on the fourth hole of playoffs, beating Rickie Fowler in 2016 and Webb Simpson in 2017.
When I was on hand, I saw a group of fans dressed up as famous wrestlers and another in a girl's dress.
He looked set to claim the solo lead on Friday until he overcooked his chip shot at the par-four 17th for a soft bogey. "We have given ourselves some pretty good chances".
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"Just solid day", Fowler said.
Players know what they're getting into every time they step into the enclosed stadium. I'm comfortable on this course. Yesterday we started on the back and got off to a decent start there and then cooled down a little on the front.
If you've never been to the Phoenix Open, let's just say it's unlike any other PGA Tour event you'll ever experience.
Ever had a par 4 ace?.
Spieth hadn't missed a cut since the Byron Nelson in May, a run of 15 straight cuts made worldwide.