And the Town manager has defended his selection for the game, which was won 3-0 by the Bantams, with all three goals coming in the first 27 minutes at Wembley.
Northampton failed to produce a shot on target and succumbed to a 3-0 loss that means they remain in npower League Two for another season.
Boothroyd felt the occasion got the better of far too many of his players, who did not perform up to their recent high standards and were convincingly beaten by a Bradford side who were in full control throughout.
“It was a culmination of a very good season going badly wrong at the end,” he said. “We did everything we possibly could to prepare and I thought Bradford’s defeat here earlier in the season would work in our favour.
“But it didn’t and they certainly started the stronger in the first half an hour. There were a few of my players out there who were unrecognisable from the lads who have got us this far.
“I don’t think there are many lads in our dressing room who can say they showed the true reflection of what they are capable of and what we’ve been about, how well we’ve done to get to here.
“We started badly and we looked like rabbits in the headlights for a while. Coming back from 3-0 down after 30 minutes is a massive uphill battle.
“We shuffled and swapped a few things around to try to get back into it but it was too much and the most disappointing thing for me is that I just wanted the group I work with every day to be the best they could be.
“I wanted them to perform as well as they are capable of performing on the big stage and they didn’t.”
Boothroyd selected two players who have not featured in the first team for more than a month, Clive Platt and Ishmel Demontagnac, and dropped leading goalscorer Adebayo Akinfenwa to the bench, although he was introduced after 55 minutes in place of a tiring Platt.
The manager said he had no regrets about the controversial selection and is aware he will face some criticism for it.
“Not at all,” he said when asked if he wished he had made a different selection. “I wouldn’t do anything differently. As a manager you have a plan for what you’ve got to do.
“If you pick a team and it wins then you’re a very good manager and if they don’t win then things are always said. That’s why football is such a game of opinions.”