Dunne is an unknown quantity to much of the golfing world, with fellow co-leader Jason Day admitting that he knows "absolutely nothing" about the Irishman.
To avoid anyone else suffering the same fate, here is all you need to know about Dunne…
He's just finished college
Dunne recently completed his senior year on the University of Alabama-Birmingham's golf team by finishing fifth in the individual competition at the 2015 NCAA Division I Men's Golf Championship. He didn't just excel on the course though, he also bagged a degree is business finance.
He's still getting tips from his old coach
His caddie at St Andrews is University of Alabama-Birmingham golf coach and compatriot Alan Murray.
He nearly didn't make it to St Andrews
Dunne, who is 80th in the World Amateur Golf Rankings, only booked his spot in the Open field by winning the final qualifying in Woburn at The Marquess’ Course three weeks ago. He was nine-under for two rounds to see off the challenge of, among others, Retief Goosen and Colin Montgomerie.
He's older than Jordan Spieth
Perhaps it's just another sign of how impressive Spieth is, but despite still be an amateur Dunne is eight months older than Spieth. For the record, Dunne was born in November 1992, while Spieth was welcomed into the world in July 1993. We're all suddenly feeling rather old…
He's been mistaken for Spieth a number of times at the Open
Paul Dunne joked earlier in week about people mistaking him for Jordan Spieth in UA gear. "I lift my head up and they are disappointed.
— Ewan Murray (@mrewanmurray) July 19, 2015
— SportsJOE.ie (@SportsJOEdotie) July 17, 2015
Under Armour are certainly getting a good deal with Dunne
Under Armour got $1.725M worth of TV ad time on Paul Dunne’s apparel today, per @apexMGAnalytics. Not bad for someone they don't pay.
— Darren Rovell (@darrenrovell) July 19, 2015
This isn't his Open debut
The 22-year-old turned out at the Open in 2014 too, but missed the cut after rounds of 75 and 73.
If Dunne triumphs at St Andrews, he will be the first amateur to win the Open since Bobby Jones. That's pretty impressive company.
He won't win any prize money
Because he is an amateur, Dunne would not receive the $1.8 million prize money awarded to the winner or the hundreds of thousands he would receive for a top five finish.
Next up, the European Tour
Dunne is planning to enter the European Tour Qualifying School later this year to earn his card as a professional.
Never leave home without a good breakfast
Born in Greystones, Ireland, Dunne is the son of Colum and Michelle Dunne and has an older brother, David, and a sister, Alison. David is a performance nutritionist with Harlequins Rugby, Queen’s Park Rangers Football Club and British Canoe, and it seems to have some benefits…
— David Dunne (@Dunne_Nutrition) July 19, 2015