"Hopefully, I can maintain where I'm at," Johnson said.
Leonard parred his last two for a 65.
"Would love to have made a few more putts," Leonard said.
Other than the 18-footer on No. 15, the longest putt Reed holed was a 5-footer for par on the par-4 13th. That was a crucial putt after he played the previous eight holes in 1 over with four bogeys and three birdies.
"I knew that if I didn't make that putt, then it was going to get interesting," Reed said. "To make that putt kind of gave me a little bit more fire saying, 'All right, well, we're running out of holes for people to make a lot of birdies.'"
Reed missed two 6-foot par putts and an 8-footer and dropped another stroke with a poor bunker shot on the par-3 12th.
"It would either just stop just short, or it would break at the very end and break off the planet and lip out," Reed said. "It seemed like nothing would go in."
On Saturday, Reed broke the PGA Tour record for relation to par for the first 54 holes, finishing at 27 under. He also became the first player in tour history to open with three rounds of 63 or better. On Sunday, he became the second player in the event to lead wire-to-wire, joining 1977 winner Rik Massengale.
"To have a day where I felt like I had probably about my C or D game and still shoot under par, and to close off a victory, that means a lot to me," Reed said.
Reed's wife, Justine, is pregnant with their first child, forcing her to turn over caddieing duties to her brother, Kessler Karain. She has walked every hole this year and plans to caddie again after the baby arrives around Memorial Day.
"I can't wait to be a dad and have a little girl running around," Reed said.
After helping Augusta State win NCAA titles in 2010 and 2011, Reed drew attention in 2012 when he successfully Monday-qualified for six events. He earned his tour card in December 2012, surviving six rounds of Q-school at PGA West.
"We have worked so hard at it," Reed said. "Especially, with my wife and I, how hard we have worked the past 2½ years, through Q-School, through the Monday qualifiers, and through here to get two wins in less than half a year."