Irwin, the defending champion, fired a nine-under-par 63 to match the course record at Greystone Golf & Country Club. Jack Kiefer originally set the mark in 1992 which was equaled by Graham Marsh in 1995, Terry Dill in 1998 and Gil Morgan last year.
Irwin bogeyed his first hole of the second round but quickly made an adjustment to his putting grip and went on a birdie tear. He collected four birdies on his front side and added six more on the back, including the last four holes.
'Birdieing the last four holes is a terrific way to finish your day,' Irwin said.
Irwin did not get off to a good start in the first round. He was two-under par in the first round and seemingly out of the competition unless he fired a low
'It was not a very good display of golf,' said Irwin, referring to his first- round performance. 'There was some pressure to get back into the tournament in the second round.'
The first round was suspended because of inclement weather Friday after starting two hours late, and play was delayed almost three hours early Saturday. The second round began as players completed their first round.
Sammy Rachels carded a 64 in the second round and is tied for third with George Archer at 10-under par.
Nelson, an Alabama native, birdied three holes in a row starting at the sixth and added three more on the back nine to grab sole possession of first place.
Nelson won five times in 2001 but has struggled so far this year. He has nursed hip and shoulder injuries and now feels like his golf game is ready to return form.
'It's exciting for me, not just for this tournament, not just for (Sunday), but there's a lot of the year left,' said Nelson, who has had only one top- 10 finish in 2002. 'I haven't hit the ball good two straight days this year, and I have definitely hit the ball well for two days this week.'
Dana Quigley, who established a new Senior Tour record for consecutive starts with No. 178 this week, is tied with first-round leader Bruce Fleisher for fifth. The duo stands at nine-under par.
Tom Kite, Bobby Wadkins, Bob Charles, David Graham, Bob Gilder and John Jacobs, who lost to Jim Thorpe in a playoff at The Tradition last week, share seventh at minus-eight.