And having to make up 18 holes by playing 36 on Friday, it seemed Father Time would have a say in how the 57-year-old would hold up and play on such a long day.
But that too didnt matter as Irwin shot 70-67 to take the lead at the Senior circuits last official tournament of the year. His 7-under 137 puts him one shot clear of Bob Gilder (68) and Gil Morgan, who also shot an afternoon 67.
Due to torrential rains that made the course unplayable on Thursday, most of the players had to make up most of their holes in the morning before getting in their scheduled 18 Friday after lunch.
Irwin was one of four players ' Gilder, Bruce Fleisher and Tom Kite were the others ' that had to make up all 36.
Irwin, who has already wrapped up the money title, played alongside Gilder. The two are vying to see which one can finish the season with a tour-leading five wins.
Irwin had 4 birdies on the front side of his inward 18, as Gilder matched him with four of his own. However, a birdie at the 10th by Irwin and a bogey at the 15th by Gilder gave Irwin a two-shot lead over his main rival.
'I played well, played very effectively,' said Irwin. 'Really the only bogey I came close to making was from a very good putt at the 16th, from 30-feet to eight, and made that eight-footer (to save par).'
Gilder responded with a birdie at the par-5 18th to close the gap to just a stroke as they head into the weekend. Gilder is the defending champion.
'I have to say I thought the golf course played easy,' said Gilder. 'I mean without any wind and the ball just stopping where it lands - this golf course really is a sitting duck.'
Two back of Irwin sits Larry Nelson, who despite 10 top-10s on the year, is still looking for his first win of the season. He had five victories in 2001.
A large group of seven players, including Fuzzy Zoeller and Tom Watson, are four off the pace at 3-under.
Full-field scores from the Senior Tour Championship