Bud Cauley, yet to win after five seasons on tour, carded a 66 to join defending championBrendan Steele (72) in a tie for third place on 12 under.
Brendan Steele won the tournament at 15-under, while Tony Finau finished at minus-13.
Steele had a big season a year ago.
John Daly, the two-time major victor who in May won his first PGA Tour Champions title and is playing via a sponsor exemption, birdied the 18th for a second-round 69 to make the 1-under cut at 143.
The last PGA Tour title won by Mickelson was back in 2013, the same year he won both the US Open and The Open Championship. "I made 17 greens out there, left myself in some good spots, made a few of them and it was just kind of easy out there". That was a strong 3-under 69 on Sunday, but that double bogey may haunt him for a bit.
He said: "Let's take a moment to admire the fact that I just hit a fairway". Errant driving throughout the week perhaps cost the Hall of Famer his 43 PGA Tour victory.
John Daly, the two-time major victor who won the PGA Tour Champions Insperity Invitational in May, had a 74. He has never finished in the top 10 in a Grand Slam event. "Lots of holes into the wind, lots of uncomfortable shots".
"I was hitting great shots, good putts and got some good breaks". There are a couple of tee shots and a couple of approaches where you have to pay attention.
He added an eagle on the fifth but followed with a bogey on the next hole.
Finishing tied for third were Phil Mickelson and Chesson Hadley at 12-under par, with the latter shooting a 1-over par 73 on Sunday. He had a back-nine 30 with six birdies.
3 - It was a hard final round for Tour rookie Tyler Duncan.
Back-to-back birdies on the ninth and 10th were cancelled out by dropped shots on both the eighth and 15th.
Duncan is now 9/2 joint favourite alongside Chesson Hadley, who shot 70 to move within a stroke of the lead.
The current leader Tyler Duncan was tied at the top after the first round but bogeyed on the second, third and fourth to sit at one under for the day after four second-round holes on the front nine. Daly has missed the cut in 12 straight PGA Tour events.