DeChambeau shared the lead with Brooks Koepka overnight after both men came home in 31 to complete opening rounds of 66.
A wild start to Day 2 for Koepka saw the three-time major champion start birdie, double bogey, birdie before dropping further shots at the fourth and sixth holes.
Koepka claimed his third birdie of the day at the par-5 eighth to get back to 5 under, leaving him one behind DeChambeau, who mixed two birdies with two bogeys on his opening nine to retain a slender lead.
Open champion Molinari and former world No. 1 Day were also only a single stroke behind the leader, having both turned in 33 to be 5 under for the tournament. Day’s efforts were particularly impressive given he has been struggling with a back injury this week.
Patton Kizzire went around in 70 to hold the early clubhouse lead at 4 under, with Phil Mickelson and Ian Poulter alongside him on the leaderboard and Dustin Johnson among those one shot further back.
The likes of Tiger Woods (minus-2), Rickie Fowler (minus-2) and Rory McIlroy (plus-1) were about to begin their second rounds.
