When the U.S. Senior Open begins play Thursday at SentryWorld in Wisconsin, among the 156 competitors will be 10 past U.S. Senior Open champions, five former U.S. Open winners and 23 past USGA champions.

The field is stacked with the game’s top players over 50, including stars Ernie Els, Jim Furyk, Padraig Harrington, Steve Stricker and Bernhard Langer.

Also in the field among that golfing royalty will be Mark McCormick, a 60-year-old New Jersey club pro who got into the field via qualifier at Arcola Country Club, where 150 players competed for four spots.

For McCormick, the longtime head professional at Suburban Golf Club in Union, N.J., who’s carved out a decorated playing career in the New York/New Jersey Met Area, this will be the third major championship in which he’s played.

On his 24th and final try, at age 49 he qualified for the 2012 U.S. Open at Olympic Club, and in 2017 he qualified for the U.S. Senior Open at Salem Country Club in Massachusetts.

This one, though, might be the most unlikely for a few reasons. First, his age. At 60, he’ll be one of the oldest players in the field. Second, he’s pretty busy with his day job at Suburban so he doesn’t have much time to work on his game. And he was recently inducted into the New Jersey PGA Hall of Fame, seemingly a capper to a fine career.

But McCormick is a club pro who belies his birth certificate and is constantly quietly tinkering to get better, age be damned, whether it be with his diet, his swing technique or his equipment.

“I don’t really think he’s ready to stop playing — at least competitively,’’ McCormick’s son, Ryan, who plays on the Korn Ferry Tour, said. “I’ve seen from him in the last year or so still wanting to get better and still wanting to improve at age 60, which is so awesome.

“He still has passion to play and to get better and to be competitive. I don’t know that there’s that many guys at this stage in their careers that still have that.’’

Ryan McCormick called his father qualifying for this Senior Open a “pretty incredible’’ achievement.

“I thought that he would kind of pack it in after the Hall of Fame thing, to be honest,’’ Ryan said. “For him accomplishing the things he has in his career — playing in the U.S. Open, playing in a Senior Open before, playing in all the New Jersey tournaments and having a great career — I figured that was kind of the sun setting on his career.’’

McCormick is so low-key about everything he does that after shooting 73 in a morning round in the qualifier at Arcola, he drove down to Hollywood Golf Club to play in the annual “Clambake,’’ a New Jersey PGA section tournament.

He was on the seventh hole at Hollywood when Ryan, who’d been tracking the scores, called him on his cell phone and implored him to drive back up to Arcola in case there was a playoff.

McCormick recounted the phone call, and he copped to his casual attitude.

“He’s like, ‘You need to get your ass back up to Arcola, you might have a playoff and a chance it make it … how many more chances will you get to play in a Senior Open?’ ’’ McCormick recalled.

“He’s 60 and he just got inducted into the Hall of Fame and there’s not that many years left of golf that he’s going to be competitive in,’’ Ryan said. “He might not see that, but I see it. It’s just the facts of how old he is.’’

McCormick said Ryan “was more excited for me than I was’’ about making it into the Senior Open.

“He pushes me more than I push myself,’’ McCormick said.

Ryan said his plan is to work with his father until Wednesday when he drives to Illinois, where he has a Korn Ferry event. McCormick’s youngest son, Mark, who works for the USGA, will be there, as will Mark’s wife, Linda. Mike Schneider, a former caddie at Suburban and the son of a former member, will caddie for McCormick in the tournament.

As the event has drawn closer, McCormick acknowledged the thrill of being a part of it.

“I would consider the U.S. Open still much more of an accomplishment than making Senior Open, but to make a Senior Open a second time at 60 years old, that was pretty cool,’’ McCormick said. “I thought maybe my days of qualifying for a national championship were pretty much over. But my game has kind of been pretty good.’’

McCormick didn’t make the cut at either of the previous two majors he played and said, “I feel like making the cut would be quite an accomplishment, and I feel like I’ve got it in me.’’