Jay Haas, making his Champions Tour debut, capped a 2-under 69 to climb into second place at 6-under-par 207. Canadian Dave Barr and former U.S. Amateur champion John Harris share third place at 5-under-par 208.
The resumption of the Senior PGA's third round was delayed until 12:00 p.m. (ET) Sunday due to overnight rain that again soaked the course. There have been delays every day due to weather.
Irwin, who also lead after the second round, parred the first nine holes of his third round Saturday before play was halted for the night due to darkness. The three-time Senior PGA winner parred Nos. 10 through 12 when he returned to Valhalla Golf Club on Sunday.
Irwin then dropped in a birdie at the par-4 13th to get to 7 under. After four straight pars, the 58-year-old two-putted for birdie at the par-5 closing hole to take a two-stroke cushion to the final round.
Haas returned to the course Sunday and picked up a birdie at the par-3 11th to move to minus-5. He then birdied the par-4 17th to take solo second place entering the final round.
Harris, who is playing with Irwin, bogeyed the 10th to slip to minus-3. He erased that error with a birdie at the 13th. After three straight pars, he dropped another stroke at the 17th.
Harris closed his round in fine fashion. His second shot to the par-5 18th lipped out of the hole and stopped inches from the cup. He tapped in for eagle to close an ever-par round of 71.
Barr picked up two birdies and a double bogey over his final nine holes to cap a round of 2-under 69.
Tom Watson stands alone in fifth place at 4-under-par 209. Craig Stadler is one stroke behind him at minus-3.
Vicente Fernandez, D.A. Weibring and 2002 Senior PGA Champion Fuzzy Zoeller are tied at 2-under-par 211.