There were three places up for grabs at Mount Juliet Estate and while tournament winner Lucas Herbert and third place finisher Johannes Veerman's places rarely looked in doubt, Karlberg snatched a ticket to Royal St George's Golf Club right at the death.
Having gone out in the penultimate group of the day and been the penultimate player into the event, the Swede was two under for the day and three shots off the mark that could potentially send him to the 2021 Race to Dubai's final Major Championship stood on the 15th tee.
But he put an approach to four feet for birdie and with Scot Grant Forrest making a double bogey on the last, the door was slightly ajar.
He got up and down for another gain on the 17th and with Francesco Laporta also making a six after finding the water on the 18th, Karlberg was suddenly in the box seat.
Sitting in the greenside rough, he knew an up-and-down would be enough but he duly holed his chip for a 67 and sealed a third Open appearance and sixth Major start of his career.
"Right away when I saw that ball, like I have some stuff behind it but I know how to hit it and if I land it there - somehow it just popped in my mind to hole it and it went in," he said.
"It's just crazy, this game. I mean, I'm into the tournament because a few guys were on a flight from America and it was from that the UK, they had to quarantine.
"You get the opportunity and you take care of it and at times you feel bad for the other guys because it's been really stressful this kind of thing we're going through, even if we're really happy with playing, it's stressful.
"And so with that said, I'm so happy."
Herbert will be playing his second Open after making the cut on his debut in 2018, and will be teeing it up in his seventh Major Championship.
"It's awesome when you get to play an Open Championship," he said. "Some of the best venues in the world and they test you so much strategically.
"I haven't played the course before. There's always a great buzz around The Open. Everyone gets behind it in the UK and Ireland. I'm stoked to get that start.
Veerman is playing his second Major after coming through qualifying in Dallas for last month's U.S Open, where he missed the cut.
"Playing the oldest championship in golf, it's a dream come true to play the British Open," he said. "I feel so blessed to be playing in it."