Purtzer, a five-time PGA TOUR winner, shot a 3-under 67 to go to even-par 140 for the tournament. That put him one up on Jay Haas, the first-round leader, who shot a 2-over 72, and Massy Kuramoto, who finished the day with a round of 2 under.
Mark OMeara scored the tournaments low round of 66 to jump into a tie for fourth with Bernhard Langer at 142 in the $2 million event.
While temperatures warmed to above 60 on Friday after a bone-chilling and wet opening round, a tricky and persistent wind played havoc with competitors along the East Courses narrow and well-protected fairways.
Purtzer was one of only eight players to post a sub-par round in the first two days, including Haas 1-under on Thursday.
There were 26 players within 6 shots of the lead. Greg Norman, Scott Hoch and defending Senior PGA champion Denis Watson were part of a 10-player logjam at 145.
The cut was established at 12 over, leaving a field of 84 players heading into the weekends final two rounds. Among those missing the cut were four-time Senior PGA champion Hale Irwin, who was 15-over after two rounds, and Fuzzy Zoeller (13-over).
Purtzer, a six-year Champions Tour veteran, had an efficient round, carding five birdies and only two bogeys. Hes posted only two top-10 finishes this season, and is seeking his first win since the 2007 AT&T Classic.
Haas, meanwhile, stumbled in a round that included a double-bogey on the par-3 No. 15. His 2-over ended a string of three straight sub-par rounds at Oak Hill, dating to his final two rounds during the 2003 PGA Championship.
OMeara created a buzz with his 66 on a course that had only three PGA TOUR players shoot 66 or better in 2003: Chad Campbell shot a 65, while Phil Mickelson and Rod Pampling both shot 66.
Bouncing back from a wildly inconsistent opening round, which included three double-bogeys and one triple, OMeara settled down by carding six birdies on Friday. The best came on No. 13, where he holed a 25-foot putt. He then completed his day by holing a 12-foot putt to save par on No. 18.
OMearas 4-under came from out of nowhere, considering hes managed only two top-10 finishes on the Champions Tour this season and after having no success in his previous two visits to Oak Hill. He missed the cut at the PGA Championship five years ago and at the 1989 U.S. Open.
Without going into much detail, OMeara blamed his struggles this year on a personal issue, which he later referred to as a relationalship thing.
Its been a tough year, said OMeara, who won both The Masters and British Open in 1998. Today, I felt my patience and attitude were a little bit better. I tried to stay more in the moment.