Reed had six birdies in a bogey-free round that was a stroke shy of matching his best of the year.
John Huh had the best round of the day a 62 to move to 10 under. John Deere winner Jordan Spieth was 9 under after a 66. Spieth also is a PGA Tour rookie, and Huh is in his second year.
Organizers moved up the third-round tee times Saturday to try to dodge a threat of rain, with players going off in threesomes at the first and 10th tees.
Reed, the 23-year-old former college player at Georgia and Augusta State, had top-10 finishes in his last two tournaments. He could have built an even bigger lead in this one, but missed a 12-foot birdie putt on the par-3 seventh.
He closed his round with birdies on the eighth and ninth holes, sinking a 10-foot putt to applause from the gallery and walking off the green with his arm around Justine's shoulder.
She began caddying for him last summer before a Monday qualifying tournament in Houston. During a humid, 100-degree day in Texas, she had no trouble lugging around a bag full of rain gear, he said.
"I told her to read putts for me that day, and she just has a knack for reading greens extremely well," Reed said. "It's basically like my coach being out there with me. She knows just as much about the golf swing. She knows why I hit it left or right or anything like that, so I mean, if ever I get out of whack, she can fix me immediately."
Kenny Perry shot a 7-under 65 to take a one-shot lead after the first round of the Dick's Sporting Goods Open at Endicott, N.Y.
Perry sank a birdie putt at No. 18 to move ahead of brothers Brad and Bart Bryant and Joel Edwards.
Esteban Toledo, Jeff Freeman, Rick Fehr, and Russ Cochran were tied at 67 as just over half the field broke par under ideal scoring conditions at En-Joie Golf Club.
Patrick Reed -11
John Huh -10
Jordan Spieth -9
Six tied at -7
Daniel Summerhays +1
Mike Weir +4