However, as the victory sank in, other thoughts and emotions began to bubble to the surface.
The eighth-grade dropout who taught himself to play golf with a beat-up 5-iron, who won bets on a par-3 course by hitting balls 100 yards with a taped Dr Pepper bottle, who had been making $30 a week five years earlier as an assistant pro in Texas, now - finally - felt that he fit in.
"I will say this to you," Trevino, 73, says today. "Merion gave me my career. Up until Merion, the way this played out, I never felt comfortable. I never thought that I belonged. I was a professional golfer, and I had won a few tournaments, but I didn't really feel like I was in the fraternity.
"So when I got into the playoff and I beat Jack, 68 to 71, I beat the best player in the world, head-up. When I walked away from there, what I took away was, it wasn't so much that I had won the Open for the second time, it was who I defeated to do it. It finally made me feel like I belonged in the fraternity.
"I played a tournament in Cleveland the next week, and I'll never forget this: Bob Goalby ran two fairways over to shake my hand and tell me he was really proud of me and that I did a hell of a job. That meant a hell of a lot to me. Goalby was one of the rough ones out there, a tough one. He was the one you couldn't get close to. So I appreciated that coming from him. For the first time in my life, I felt like I was part of the deal. Part of the deal."
The U.S. Open at Merion was one of six major championships won by Trevino - two Opens (1968, 1971), two British Opens (1971, 1972) and two PGA Championships (1974, 1984). Amazingly, the 1968 Open and the 1984 PGA were the first, and last, victories of his PGA Tour career.
In all, Trevino, who was elected to the World Golf Hall of Fame in 1981, won 29 tournaments and nearly $3.5 million on the regular tour, and 29 more events and $9.86 million on the Champions Tour.
He did it with a homemade swing he once described as resembling that of "a caveman killing his lunch." But the ball usually went straight, especially with his driver, and that's why he liked Merion's deep rough at first sight, even if he joked he was going to carry a gasoline can with him during his rounds to burn it down to a lower height.
"I fell in love with that golf course because it's not a monster," he said. "You have to understand that I'm a Texas boy. I came off a farm. I never got to play really great golf courses. I never went East. I played public courses in Dallas my entire life. So when I saw Merion for the first time ... all those holes were just absolutely magnificent. Everything was perfect about it. I loved the tall rough; it would really penalize you back in those days.
"I hit the ball really, really straight with my driver. When I get to a golf course that's small and tight and the rough is extremely high, it's to my advantage because I'm not scared to hit driver. Most of the big boys are scared to hit driver; they hit 3-wood, 5-wood, or 1-iron off the tee. It also gave me an advantage that I was a better wedge player than most of them. Plus I had won the Open in '68 so I was pretty confident in that particular tournament."
Trevino overcame a rough patch on the second day at Merion to stay within striking distance of the lead. After three rounds, however, he trailed Butler, Pa., amateur Jim Simons, the 54-hole leader, by 4 strokes. Nicklaus was 2 behind Simons.
Trevino surged into the front in the final round and held a 1-stroke lead on the 18th tee. But his second shot bounced off the back of the green and into trampled-down rough, and his pitch stopped seven feet from the hole. After backing off his par putt when he heard a noise in the gallery, Trevino missed to fall back to even par.
Nicklaus one-putted the 16th and 17th holes for pars and stuck his approach at the last to 15 feet. The downhill birdie putt missed the cup by maybe two inches, and the 18-hole playoff would commence the next day at 1:45 p.m.
Perhaps the greatest memory of golf aficionados in the playoff was not any one specific shot, but the rubber snake in Trevino's bag that he playfully tossed to Nicklaus before the pair teed off.
And no, insists Trevino, the snake had nothing to do with gamesmanship or gaining an advantage. Nicklaus actually had asked to see it.
"The snake was used to show how deep the rough was," he said. "We did that on Tuesday or Wednesday and it was in Sports Illustrated and the local newspaper. I put the snake in the big pocket [of my bag].
"When we got to the tee, it was extremely hot, and my glove was sweated out, so I reached into the big pocket to get another. The snake was in there so I pulled it out and showed it to all the people. Jack was sitting across the tee on this little stick seat and said, 'Throw it over here, let me look at that.' So I threw it over to him, and I guess some people didn't see him say that. I would have never thrown it over there if he wouldn't have asked for it."
Trevino dropped 1 stroke right away at No. 1 after hitting his approach into a bunker, but that would be his only bogey. He pulled even at the par-5 second where Nicklaus bogeyed, and then went ahead by 2 when Nicklaus needed 2 strokes to get out of a bunker at the par-3 third and made double bogey to Trevino's par.
Trevino never trailed again. Nicklaus cut the deficit to 1 stroke three times, the final occasion with a birdie at No. 11. But Trevino drained a 20-footer for birdie at the 12th to go up by 2, then increased his margin at the par-3 17th when he sank a three-foot putt to save par while Nicklaus bogeyed.
Now leading by 3, Trevino took nothing for granted as he walked to the treacherous 18th.
"The out-of-bounds was extremely close to the left side there," he said. "I figured the only way I would lose was if I hooked it out of bounds and made 6. He makes 3, and we have a sudden-death playoff. So I was very careful where I put that ball. I put [my second shot] in the front bunker and came out about three feet and holed the putt.
"You know, in a sudden-death playoff, a ball can bounce off a rake or you can chip in. But 18 holes, I like that. In my opinion, no major championship should be determined by a sudden-death or a three-hole or a four-hole playoff. Your sponsors and all the people there want to see a champion that day. But a major should go 18 holes."
Time has passed
While he participates in numerous golf outings, Trevino doesn't compete any more. He works out every day and conducted this interview while walking on a treadmill. He hits practice balls daily and raps some putts on the green in the backyard of his Dallas home. He also works with his son on his game. He is finishing his sophomore year at Southern California and may walk onto the golf team next year.
Trevino misses the competition, but he knows his time has passed.
"I've come to grasp the reality part of it," he said. "but it doesn't keep me from dreaming, you understand what I'm saying?
"I go to hit golf balls and watch the ball go out there and say, 'Man, I can still compete.' But you're hitting wedges 150 yards, and I'm hitting them 80. People ask me, 'When did you know you couldn't compete any more?' I said, 'It's when I was hitting a hybrid from 120 yards.' That's when I knew."
This is a big year for Trevino. The 2013 majors are being contested on three of the courses - Merion (U.S. Open), Muirfield (British Open), and Oak Hill (PGA) - at which he won championships. He is in much demand for interviews, or as he puts it: "I haven't shut up in 21/2 months."
Trevino returned to Merion for the 1981 U.S. Open, but the memories weren't quite as good. He missed the 36-hole cut after rounds of 72 and 76, and hasn't been back since.
He will come back to Merion for a dinner on the Tuesday of Open week in June, followed the next day by golf at Pine Valley. He called it "wonderful" that the U.S. Golf Association has brought the Open back to Merion.
"The USGA is going to prove once again that they can go to a shorter course if it's prepared correctly, and if they can control the water to it, they can challenge any golf professional in the world," he said. "You don't have to have a golf course that's 7,600 yards long and all tricked up. My hat is off to the members for letting the USGA come in for such a great championship."
And he's happy for being allowed to share his memories.
"We're having our 15 minutes of fame again," he said with a hearty laugh. "After 42 years, and 25 pounds heavier, we'll have our fame again, you know what I'm saying?"
Contact Joe Juliano at firstname.lastname@example.org. Follow on Twitter @joejulesinq.