Bob Gilder is alone in fourth at 9-under par, followed by Bob Charles, who bested his age by two strokes with his second-round 65, and Jim Colbert. That duo is minus-8.
Irwin, who held a one-shot lead after the first round, started strongly at the Greystone Golf and Country Club. He knocked his third shot at the par-5 second hole to four feet to set up birdie then holed a 15-footer for birdie at the next hole.
Irwin, the all-time leader in wins on the Champions Tour with 36, took advantage of the next par-5, the fifth. His sand-wedge approach stopped six inches from the cup and Irwin kicked in his third birdie in five holes.
The 57-year-old went on a dry spell after the birdie at five. He parred the next seven holes but it was once again a par-5 where Irwin broke into the red.
At the 531-yard 13th, Irwin pitched his third to six feet where he converted for birdie. He played a 7-iron to 15 feet at the 16th for his fifth birdie of the round but it was his play at the par-3 17th that kept him atop the leaderboard.
Irwin left himself with four feet to save par at the 201-yard hole but he calmly rolled home the putt to keep his one-shot advantage on Fleisher and Jenkins.
'I'm not unhappy with my score, but when you birdie three of the first five and then make only two more birdies the rest of the day, you're a little disappointed,' Irwin said. 'It was another bogey-free round today, which meant I didn't give one back.'
Irwin is winless thus far in seven starts in 2003. He held the 36-hole lead at the Verizon Classic but Fleisher overtook Irwin in Sunday's final round.
'All in all, I'm pleased,' Irwin said. 'I'm certainly looking forward to tomorrow. I don't mind being in the lead. Sometimes I think it makes me concentrate more, makes me put the pedal down a little harder.'
Fleisher was 1-under through his first nine but turned it on during the second nine. He sank a 25-foot birdie putt at 11, then made a pair of 20-footers for birdie at 13 and 14. He knocked a 6-iron to eight feet at the 16th then saved par at the 17th.
Fleisher had a chance at matching Irwin in the lead at 18 but his birdie putt slid by the hole. Still, Fleisher will be in the final group with Irwin on Sunday and has a chance to become the first multiple winner of 2003.
'Hale is the best,' said Fleisher, who had a 67 on Saturday. 'That's why you're out here, to be in the same threesome as him. To be in the same pairing with him on Sunday, it doesn't get any better for me.'
Jenkins flew out with three birdies in his first five holes but missed two good birdie chances around the turn. He played a pitching-wedge two feet from the hole for birdie at 11 and holed a 10-footer for birdie at the 13th.
He missed the green left at 14 and bogeyed the hole but Jenkins tallied two more birdies on the way in for a round of 6-under 66.
'It's going to be a good day tomorrow,' said Jenkins. 'I enjoy playing against Hale and Bruce. It will be a fun day.'
Rodger Davis and John Jacobs share seventh at 7-under par, followed by Frank Shikle, Dave Barr, Bob Murphy, Tom Wargo and Graham Marsh, who are tied for ninth at minus-6.