Jason Dufner survived two back-nine bogeys to take a one stroke lead over fellow American Zach Johnson into Sunday's final round of the Colonial Invitational in Fort Worth, Texas.
Johnson narrowly missed sharing the top spot when his 12-foot birdie putt fell inches short at the 18th hole.
Dufner, seeking his third PGA Tour victory in five tournaments, used six birdies to offset bogeys at 14 and 16 for a four-under 66 and 195 total.
Johnson carded a five-under 65 to finish a stroke back.
The 2007 Masters champion pressured Dufner throughout the hot day, using a birdie at the par-three 16th that Dufner bogeyed, to move within one.
Dufner steadied himself to join Johnson in a birdie-par finish to hold onto the lead.
Americans Tom Gillis (203), Bo Van Pelt (204), John Huh (205) and Ryan Palmer (205) rounded out the top six.