The 25-year-old, who had played only one competitive tournament 12 months previously, had to battle his way from behind to get his hands on the prestigious piece of silverware that remains the oldest trophy in professional golf that is still contested.
McCullen, who was also making his PGA tournament debut, had begun his second round on level-par, three shots adrift of the leader, Renishaw Park Golf Club’s Michael Ramsden, winner of the famous old trophy in 2017.
Others in the mix to claim the £2,000 first prize were Staysure Tour winner David Shacklady, previous Leeds Cup victors Jason Shufflebotham and Garry Houston as well as defending champion Gareth Davies.
McCullen served notice of things to come early on the second day with a birdie at the par-four first. Another birdie followed at the par-three ninth to take him to two-under at the turn. He then added another three at holes 11, 15 and 16 for a five-under-par bogey-free round of 64. All of which left the chasing pack two shots adrift and pondering what might have been.
“The aim was to find the fairway off the tee and keep out of trouble,” he explained after his achievement. “I only used the driver six times in the two rounds and, aside from the par-threes, otherwise teed off with a three-iron.
“I may have been 20 to 30 yards behind most of the others off the tee but I felt it was worth sacrificing distance in the long run.
“There were some formidable players out there – Shackers (David Shacklady), Garry Houston and Gareth Davies – so I’m delighted to finish ahead of them and to add my name to such a distinguished list.
“As for the future – I’ve had a few injury problems which have held me back so hopefully I can build on this.”