Sean Knapp tried to explain how, after competing in 40 previous USGA championships and losing twice in the semifinal round, he could be so calm in his first championship final, for the 63rd U.S. Senior Amateur.

“For a guy like me, getting [championship] exemptions is so important, so I knew what making the semifinals brought,” said Knapp, 55, of Oakmont, Pa., who was competing in his first U.S. Senior Amateur. “I also knew what making the final brought. Once I had done that, I said, look, all we’re playing for today is the championship, and while that is an enormous thing, at the same time, I was very relaxed, very calm. I don’t know why, the whole day it was the calmest I was in any match.”

That calmness translated to victory when Knapp converted a 20-foot par putt on the 17th green at The Minikahda Club to give him a 2-and-1 victory over Paul Simson, of Raleigh, N.C., a two-time champion who would have become the fifth-oldest winner had he prevailed on Thursday at age 66. Instead, Knapp finally broke through after semifinal-round losses in the 2008 and 2010 U.S. Mid-Amateurs, his farthest advances in USGA play. He also topped Simson for the first time after Simson had come out on top in two previous matchups: a U.S. Open sectional qualifying playoff and a U.S. Mid-Amateur quarterfinal match, both in 1998.

“The last two times in the Mid-Am in [2008 and 2010], I got to the semis, and then in 2012 I lost to Nathan [Smith, Knapp’s best friend and a five-time USGA champion] in extra holes in the final 16,” said Knapp, a 14-time Player of the Year in Western Pennsylvania. “He went on to win, and I really felt like it was so tough to accept that. I knew what to do to beat him, and I did everything but beat him. I just said, if I get in this situation again, I’m going to put the throttle down.”

Throttle or not, Knapp stayed calm when opponent Simson birdied the first hole for a 1-up lead. Knapp, 55, responded with a winning par on the second hole. Twice more he calmly responded and brought the match back to even after Simson made birdies – both on par 5s, No. 4 and No. 9.

Simson’s bid to join Lewis Oehmig, the only three-time champion of the U.S. Senior Amateur, went awry on the incoming nine, just after he had taken his third and final 1-up lead of the match with the birdie on the ninth. Knapp drew even for the third time on the next hole, then took his first lead on No. 11. In both instances, Knapp missed the green and converted the up-and-down, while Simson hit the green and three-putted, running his first putt past on No. 10 and leaving it well short on No. 11.

“You know, the putting on 10 and 11 just left me there, and I just didn’t make any putts,” said Simson. “Normally I make a lot of putts. It was just one of those unfortunate days.”

Simson squared the match for the final time on No. 13, making a 5-foot putt for his third birdie on a par 5 after Knapp had missed from 8 feet away. Then a couple of Simson miscues while Knapp was making solid pars brought the match into Knapp’s favor. Simson missed the 14th fairway to the right, and his approach shot clipped a branch and ended up in thick rough short and left of the green. Simson wedged out to 14 feet and missed his par try, while Knapp got up and down from in front of the green.

On the 410-yard par-4 16th, both players drove into the rough, and Knapp missed the green hole-high to the left from an awkward stance. Simson failed to extricate his shot from the rough, which snagged his clubface, and he left his third shot in the fronting bunker. After Simson missed his bogey putt, he conceded Knapp’s short par putt.

“I probably made a tactical error on 16,” said Simson, who won the U.S., Canadian and British Senior Amateur championships in 2010, the only man to do so in the same year. “I went and practiced that tee shot yesterday after my match because I had had problems with it, and just hit a real stinker there. Maybe if it was stroke play, I would have laid out and tried to make 4 the other way, but I thought maybe I had a chance to hit a good shot out of there and it didn’t come out of the grass very well.”

When Knapp got up and down from the front bunker on the par-4 17th after Simson missed a long birdie try, the match was over. Knapp became the latest 55-year-old to win and the first newcomer to win since Louis Lee prevailed in 2011. Again, Knapp gave a nod to his friend Smith.

“Nathan and I have played so much against each other and with each other,” said Knapp, a graduate of Indiana (Pa.) University, where he played basketball. “There’s a formula, and I’m well aware of it. I can’t always execute it. He can. It’s about being patient, not giving holes, and forcing your opponent to get uncomfortable. If you can force them into that level of uncomfortability, they might make poor decisions. I’m not saying that that’s what happened today, but certainly it kept my emotions at bay.”

Calmness despite the circumstances helped Knapp become the first champion to win the title without making a birdie since Mike Bell, in 2006 at Victoria National in Newburgh, Ind. While Simson was making four birdies, six pars, six bogeys and a double bogey in a topsy-turvy round, Knapp had 16 pars and one bogey, with six of the pars winning holes.

When told that he had prevailed without a birdie, Knapp’s calm demeanor retreated for just a moment. Pointing to the Frederick L. Dold Trophy, he said, “I’ve got this big thing over there that says W. I don’t care how it looks or what it is. If you’re making double bogey, I’m going to make bogey. If you’re making par, I’m going to try to make birdie.”

On this day, Knapp was making himself into a USGA champion.

Ron Driscoll is the manager of editorial services for the USGA. Email him at rdriscoll@usga.org.