But the only thing near to a shock at Newlandsfield was that Carlo Monti had nothing to do with this dramatic finale after taking centre stage for the previous 90-plus minutes with a truly outstanding display capped by his exquisite lob for the game's opening goal.
Beith's defenders could do little about the highly-mobile Monti as he popped up here, there and everywhere, demonstrating great touch composure and no little bravery in Lok's 3-2 victory.
Their Ayrshire opponents had been rocked by a pre-match selection blow when arguably their own most effective attacking threat – speedy striker Kenny McLean – called off with a back injury caused at work on Friday afternoon.
The visiting Mighty made light of this setback in starting the better of the two combatants and it was distinctly against the run of play that they found themselves 1-0 behind in 19 minutes.
A long ball played forward by Brian McGinty found Monti criminally unmarked and in acres of space between Beith central defenders John Sheridan and Gary Wild.
An initial controlling touch was sublime and he followed this up with a touch of genius in executing an 18-yard lob that dropped into the net beyond the despairing fingers of goalkeeper Adam Strain.
Beith got back on level terms just after the half-hour mark as Mark McShane nodded down a corner kick which Andy Reid acrobatically hooked over his own shoulder and into the net from close range.
That man Monti had kept another serving of skill for the concluding minutes of the first half after he pounced on another raking pass forward to beat two opponents and fire in an angular shot that looked like it was going in at the far post before team-mate Tony Fraser applied the final touch.
Not surprisingly, Pollok seemed content to sit on their slender advantage and hit on the break as the second period got underway and Beith were allowed to get up a full head of steam in their search for an equaliser.
The home team survived by the skin of their teeth until McShane rose to head home Wild's cross for 2-2 in the first minute of stoppage time.
Opposing supporters even began to exchange handshakes and arrange terracing get-togethers for a Bellsdale replay, however this cup-tie had a final sting in its tail.
A diagonal Ross Hepburn pass picked out McCardle on the run and he let the ball bounce before smashing a low volley across Strain and into the far corner of his net.
Moments later the final whistle sounded to spark contrasting scenes of despair and delight with nobody smiling more than 22-year-old Monti.
As he looked forward to Thursday night's fifth-round draw on Radio Clyde, he said: "One or two of the lads thought my shot was over the line for our second goal, but Tony said it wasn't and that is good enough for me.
"To be honest, I don't care who scores as long as Pollok are into the next round, though I did take satisfaction from my goal as I'd only a split-second look at their keeper before deciding to have a go at lifting the ball over his head so I'm just thankful it went in."
Beith marksman McShane said: "It's so heartbreaking to lose in that fashion.
"I'd felt relieved at levelling matters because it made amends for failing to keep tabs on Fraser for Pollok's second goal though he was practically on our goal-line when touching the ball home and looked well offside to me."
His disappointed gaffer Frank Lynch also commented on Lok's contentious score.
"It goes without question that two big decisions by the same linesman, allowing a debatable goal for Pollok and denying one for Beith, has had a huge impact on the result," he said.
"But I'm not going to try and pull the wool over people's eyes by making an issue over those calls or by pointing to the barnstorming finish put in by our players.
"What those guys put in over the previous 70 minutes was not up to the standards they have set since I came back to this club and we are out of the cup because of it.
"We made mistakes, particularly in defence, and were made to pay for it by a player of Monti's quality."