Steve Stricker appeared in total command at the top of the leaderboard as he neared the turn at the Memorial.
Stricker birdied five of the opening eight holes to increase his lead to four shots over Matt Kuchar and Brandt Jobe.
They had both taken advantage of a huge wobble from Jonathan Byrd, who began the day in second place but tumbled into a tie for seventh after a bogey on the third and a double-bogey on the eighth.
That pushed Kuchar and Jobe up a place as they both made the turn at five under par on the day, 13 under for the tournament.
Gary Woodland was also on five under for the day after 12 holes, moving into a share of fourth place alongside Rory McIlroy who had six birdies but also two bogeys after 11 holes.
Dustin Johnson held sixth place on 10 under for the tournament, while John Senden and Webb Simpson were tied with Byrd in seventh.
Kevin Streelman signed for a six-under 66 to move into the top 10.
Further back, Phil Mickelson completed his round in 67, his best showing of the weekend by far, and was tied for 13th, along with Luke Donald who was three under for the day with two holes remaining.