Burnley slipped out of the Capital One Cup at the first hurdle as Port Vale took a Championship scalp.
Byron Moore grabbed the solitary goal with eight minutes remaining to settle a scrappy encounter at Vale Park.
The Clarets best chance of a disappointing night came when Michael Kightly forced a second half save from Jak Alnwick.
And despite a late flurry, there would be no repeat of the Elland Road heroics as Burnley were left to rue a below-par performance.
The Clarets made four changes to the side that opened the season with a 1-1 draw at Leeds United.
Matt, Gilks, Stephen Ward, Matt Taylor and Sam Vokes all started as manager Sean Dyche kept to his promise to shuffle the pack.
And with Vale determined to start on the front foot, it was a testing opening half for the Clarets.
Enoch Andoh, in particular, was a livewire, and the diminutive winger had the first attempt with a volley that fizzed over the angle.
Other than that, the opening 30 minutes was a scrappy affair, punctuated by petty fouls and three yellow cards.
Michael Kightly had Vale stopper Jak Alnwick scampering to claw away a deep cross from Burnley’s first meaningful foray forward.
But the hosts ended the half as they began, pushing Burnley back and forcing some excellent defending that kept Gilks quiet and the game scoreless at the break.
It took an hour for Burnley to finally get behind the Vale back line - and when George Boyd drove to the by-line and pulled the ball back to the edge of the area, it took a terrific block to deny Kightly.
Soon, Vossen’s acrobatic overhead kick in the area, following a half-cleared corner, was inches too high for the ever-impressive Ben Mee, this time lurking with intent at the far post.
That would be the Belgian’s last meaningful act, as he made was for Marvin Sordell.
And with Burnley now picking up the pace, Kightly stung the gloves of Alnwick after finding a few yards of space on the edge of the box.
But with eight minutes remaining, the deadlock was finally broken as Byron Moore drilled home a loose ball following a parry from Gilks.
The Clarets appealed in vain that the ball had not cross the line, but after consulting his fourth official, Trevor Kettle awarded the decisive goal.
There were two late chances to take the tie to extra time, as first Vokes was denied at the near post.
And when Boyd drove into the side netting from a tightening angle deep into stoppage time, Burnley knew their number was up.
BURNLEY: Gilks, Darikwa, Mee, Duff, Ward, Kightly, Arfield, Taylor (Jutkiewicz 83), Boyd, Vokes, Vossen (Sordell 65)
Subs: Heaton, Jones, Anderson, Dummigan, Jacks
Booked: Arfield 31, Taylor 55, Darikwa 60
PORT VALE: Alnwick, Purkiss, Dickinson, Streete (Inniss 46), Duffy, Dodds, Foley, Moore, Leitch-Smith (Ikpeazu 71), Andoh (Kelly 80), Grant
Booked: Grant 8, Streete 32, Ikpeazu 90
Subs: Johnson, Birchall, Daniel, Brown,
Ref: T Kettle
Att: 4,634 (909)