"I feel like my game now is better than it has ever been," the 24-year-old O'Hair said after his best round of the year. "Finally, things are starting to snowball."
He played in a PGA event for the first time in 2004, finishing second to Ted Purdy, and went on to be named PGA Rookie of the Year in 2005.
This is the first time since its inception in 1968 that Byron Nelson is missing from the tournament that bears his name. He died last fall at age 94.
1996 champion Phil Mickelson is among 18 players tied for 21st place at 1-under 69.