Charlie Austin's 50th League goal and Junior Stanislas' first in a Burnley shirt were not enough to prevent the Clarets' first defeat of the season as Middlesbrough conjured up a stunning three-card trick to secure a thrilling late win.
When the in-form Austin headed the Clarets in front Eddie Howe's men looked set to continue their perfect start to the campaign.
But Nicky Bailey quickly gave a taste of things to come as he levelled just before the break.
And even though Bailey's effort was sweetly struck, it was nothing on the two goals Boro scored in the closing stages to nullify Burnley's late fightback.
Adam Reach rifled one in from 25 yards but even that wasn't the best of the lot as Stanislas' moment of glory was snatched away from him in a frenetic finish.
The Clarets' winger thought he had grabbed a point with an alert finish four minutes from the end but there was still time for Boro substitute Luke Williams to claim the goal of the night and a first League victory of the season for his team when he lashed home the winner from 30 yards.
With Martin Paterson not asked to play for the third time in eight days as he eases his way back from last season's injury problems, Sam Vokes earned his first start since returning to Turf Moor in the summer in the only change from the Clarets' side that started Saturday's win over Bolton.
But that apart it was as you were in the opening exchanges as Burnley picked up where they left off in putting the Trotters to the sword.
In a breath-taking early spell the Clarets pulled the home side all over the place to work a string of shooting opportunities.
The best came after just six minutes when Chris McCann pulled the ball back across the penalty area for Ross Wallace but on his weaker right foot the winger placed his effort wide from 15 yards.
Dean Marney, Vokes and McCann also tried their luck from just outside the penalty area before Boro made any sort of impression with Emmanuel Ledesma curling a free-kick just wide from their first serious attempt.
That sparked an improved spell from the Teessiders as on-loan Chelsea midfielder Josh McEachran began to make his presence felt and from another set-piece former Clarets' loanee Rhys Williams scuffed an effort just wide as the ball dropped at his feet on the penalty spot.
But with Austin around there is always a goal threat from Howe's side and after the striker had been given a sighter from a Joseph Mills cross he popped up again to head Burnley in front four minutes before half-time.
Marney created the opening with a defence-splitting pass for Kieran Trippier, whose cross to the near post was tailor-made for Austin to power past GB Olympian Jason Steele from six yards to make it three goals in as many games.
It looked like the perfect time to score but critically the lead lasted less than 60 seconds as Boro hit straight back, Bailey hammering home a low drive after the ball dropped perfectly for him 25 yards from goal.
Vokes almost mustered a response of his own in stoppage time as his volley on the turn was deflected over the top but the equaliser turned the tide Boro's way as they started the second half on the front foot.
Mills fired just wide as the Clarets relieved some of the pressure but with almost an hour gone Howe made a change to try and stem the flow with Marvin Bartley added to the midfield at the expense of Vokes.
The possession statistics remained in Boro's favour but Lee Grant wasn't tested until mid-way through the half when Curtis Main took aim and would have found the bottom corner but for Grant's fine left-handed save.
Suddenly Grant was central to Burnley's chance of holding out as he finger-tipped away a header from Jonathan Woodgate.
The Clarets were then given a let-off when Grant Leadbitter dragged a shot wide but the pressure continued to mount and with 12 minutes to go the Teessiders broke through again to go in front.
This time it was Reach who smashed the ball home with a stunning strike from 25 yards which flew into the top corner.
t looked a goal worthy of winning any game but was only the appetiser for the late drama to come.
Out of almost nowhere the Clarets snatched an equaliser as Stanislas opened his account for the club, following up to fire home after a McCann header had apparently been cleared off the line by Rhys Williams to seemingly secure a point.
But the Clarets have been sunk late on by spectacular strikes here before and as two seasons ago - when Tarmo Kink made his one and only impact on Teesside - Boro blasted another last-gasp winner.
Teenager Williams had barely had a touch but didn't need to find his bearings as he picked up the ball 35 yards from goal, looked up and drilled a dipping thunderbolt of a shot past Grant to bring the Clarets' unbeaten start to the season to a dramatic end.
Burnley: Grant, Trippier, Edgar, Shackell, Mills, Marney, McCann, Stanislas, Wallace (Mee 77), Vokes (Bartley 59), Austin.
Subs: Duff, McCartan, MacDonald, Stock, Jensen.
Booked: Bartley 74
Middlesbrough: Steele, Hoyte, Friend, Woodgate, Leadbitter, R Williams, Reach, Ledesma (Zemmama 69), McEachran, Bailey (Smallwood 72), Main (L Williams 85).
Subs: Hines, Halliday, Haroun, Leutwiler.
Booked: Woodgate 69
Referee: Carl Boyeson
Attendance: 15,559 (Burnley 618)