Burnley will join rivals Blackburn Rovers, Sunderland and Cardiff City in the group stages of the Premier League Cup after bypassing Watford in the final qualifying round at Turf Moor.
Defender Jimmy Dunne and Patrick Bamford scored the all important goals in a 2-0 win for the Clarets, who had been reduced to 10 men after Kevin Long was given his marching orders.
Following an almost calamitous start where Dunne's attempted clearance was stopped by Nick Pope after ricocheting back off Jon Flanagan, the hosts went ahead.
Hornets centre-back Charlie Rowan conceded the free kick after upending the impressive Aiden O'Neill, loan man Bamford's set-piece flicked up off the wall and Dunne capitalised to beat Charlie Bannister as early as the fourth minute.
O'Neill flashed an effort past the post as the Clarets took hold of the game though, moments later, the visitors should've been level.
A well-worked free kick resulted in the ball being recycled out to Rhyle Ovenden on the right hand side, Michael Folivi ghosted in-between Dunne and Long to meet the winger's centre but side-footed over from close range.
The home side were dealt a numerical disadvantage just before the half-hour mark when referee Andrew Smith brandished a red card.
With Watford's Ogo Obi threatening to race through on goal, Long impeded the striker's run by pulling back on his shirt. Smith didn't hesitate to hold his red card aloft.
From the consequent set-piece, Pope plunged low to his right hand side to turn Obi's effort around the upright.
The Hornets, coached by Harry Kewell, had won all four of their league encounters heading in to the tie and they almost levelled early in the second half.
Obi's pass caused confusion in the Clarets defence and found Ola Adeyemo unmarked on the far side of the penalty area. The winger's thunderous strike seemed destined for the back of the net until Arlen Birch stuck out a leg to divert the ball behind for a corner.
However, after that moment the away side failed to make the extra man count as they struggled to expose their opponents.
Bamford was denied by Bannister midway through the half when attempting to tuck in a rebound after the goalkeeper had thwarted substitute Freddy Yao from distance.
But the Chelsea loan man did etch his name on to the scoresheet with a quarter-of-an-hour remaining.
Brad Jackson showed full back Harry Forster a clean set of heels and centred the ball for Bamford who was brought down by Max Ryan after getting goal side of his marker.
The striker picked himself up to take on the responsibility from 12 yards out and cooly swept the penalty in to the top corner.
Michael Jolley's side saw the game out with incredible professionalism to ensure that there will be an East Lancashire derby after all this season.