And it all went to plan, at least for the first half-hour. Scunthorpe looked assured in the opening passages of play, and took a deserved lead after 15 minutes through Gary Hooper.
The Iron had come racing out the blocks and Luton could barely string a pass together. They looked nervous, but the roles reversed after that opening period ad Scunthorpe suddenly looked susceptible at the back.
Their equaliser from Chris Martin, after being played in by Tom Craddock, was against the run of play but the Hatters had grown into the game.
It could have been so different had Scunthorpe managed to extend their lead before then.
Kevin Nicholls headed a shot from Henri Lansbury off the line, while Marcus Williams forced Dean Brill into a save with a long-range effort.
United started brightly after the restart but struggled to create chances, and Luton took the lead through Craddock - who could consider himself slightly lucky to still be on the pitch after flooring Cliff Byrne in a needless off-the-ball incident before the break.
His shot from the edge of the area went through David Mirfin's legs into a bottom corner.
Scunthorpe went on to control much of the ball, but with Luton sitting back to preserve their lead chances were still hard to come by.
Lansbury went close to levelling with a close-range shot that came crashing off the crossbar, but when time looked to be running out Grant McCann came to the rescue.
The Northern Ireland midfielder lobbed Brill with a stunning shot from the edge of the area to take the game into extra-time.
Luton attacked straight from the restart and Mirfin had to be at his best to stop Claude Gnakpa getting a shot in when he was clear on goal.
But Gnakpa was not to be kept quiet for long. Just five minutes into the extra period he put the Hatters back in the lead as they capitalised on two defensive errors from the Iron.
Cliff Byrne, the Iron captain, gifted the ball to Luton's Keith Keane. Williams and Gnapka chased the ball with Joe Murphy rushing out from the Iron goal, but neither Murphy or Williams seemed willing to take responsibility and Gnapka lobbed the ball home with ease.
So, again, United found themselves fighting to save their trophy hopes.