The concentration comes and goes, and so do the aches and pains. That’s life for a 70-year-old golfer, even if you’re one of the best to have played the game, even if you’ve kept the competitive window open longer than most. Even if you’re Hale Irwin.

Playing in his 20th U.S. Senior Open, Irwin teed off Thursday morning a few weeks after a milestone birthday, hoping he can summon some good golf but knowing he is a grandfather with other things on his mind.

“There are other things in my life now that have a higher priority than golf,” Irwin said Wednesday afternoon at Del Paso Country Club. “I don’t have a bucket list, I have a barrel. Once you think in that vein, it’s kind of hard to reel in that focus to prepare the way you used to and get out there and play with that tenacity and that discipline.”

A three-time U.S. Open champion (1974, 1979, 1990) and two-time U.S. Senior Open winner (1998, 2000), Irwin’s enduring career – his 45 career Champions Tour victories are 16 more than second-place Lee Trevino – has been defined by grit, not glitz.

Opens have been his thing for nearly 50 years, since he qualified to play his first National Open when he was a 21-year-old amateur at The Olympic Club in 1966.

“That really turned me on to what was the Open,” Irwin said. “My game seemed suited more for keeping it in play, being rather tenacious and not giving up. My football career in college really helped me a great deal.”

The former defensive back at Colorado won his third U.S. Open at age 45, and still holds the record as the oldest champion. It turned out to be a foreshadowing of his Champions Tour dominance, as he won 16 tournaments over the 1997 and 1998 seasons.

Irwin’s last senior victory came in 2007, but he continued to contend well after that. He finished fourth in the 2011 Senior PGA Championship and third the following year. A tie for ninth in the 3M Championship last year was the 210th top-10 finish on the Champions Tour for Irwin, who has played in 445 events. He has matched or bettered his age 18 times.

But this season has been a struggle for Irwin, who hasn’t cracked the top 30 or broken 70 in seven individual senior tournaments.

“There aren’t any real apparent reasons other than I’m just not in focus the way I used to be,” Irwin said of his poor play. “I get in these situations on the golf course where I confound myself with my stupidity. And it just seems like yesterday, it was not even a problem.”

He can string together a few shots, or a few holes, that recall his best days. Then an extraneous thought will pop into his head.

“I can play 14, 15, 16 holes really well,” Irwin said, “but I get to wandering, heaven only knows what I’ll conjure up. That’s the hardest part.”

In his heyday, Del Paso, with its exacting demands, would have been right in Irwin’s wheelhouse. “My skills weren’t greater than anybody else,” he said, “but I think my ability to stay on point and not back off was equal to just about everybody’s.”

With so much past success, he is conflicted about the present. In one breath, Irwin said, “I don’t know why I’m still here,” and in the next, “I think I still have the belief that I can accomplish something in the game.”

Irwin has been an inspiration to fellow seniors and wants to continue to be as long as he competes.

“You can still perform. You still do things. You just have to have realistic goals,” Irwin said. “If I can play to the level that I really believe I can, then I’m going to contribute to somebody else that’s going to be turning 70, whether they’re amateur or pro. Then what better way to give back to the game that that?”

Between the rigors of Del Paso and the forecasted triple-digit temperatures, Thursday could be a tough day. Irwin cannot prepare the way he once did, but he did try to get ready for what was expected this week.

“My main residence is in Arizona, and I was out playing in 113, 115 degrees last week, trying to get ready for the anticipated heat,” Irwin said. “That’s not to say I’m going to handle it, but I’ve been trying.”

He knows no other way and never has.

“It’s been an awfully, awfully good ride,” said Irwin, well aware the trip is much closer to the finish than the start. “My career’s back there.”

Come Thursday, though, it will be about fairways, not farewells. A man who understood the job as well as anyone will go to work.

Bill Fields is a Connecticut-based freelance writer.