Tomas Soucek's stoppage-time volley condemned Burnley to a seventh-consecutive home defeat as Vincent Kompany's struggling side conceded two in the space of five minutes to lose 2-1 to West Ham.
For much of the second half it seemed as though Jay Rodriguez's 49th-minute penalty was going to earn the Clarets a vital win and lift them off the bottom of the Premier League table.
But an 87th-minute own goal from Dara O'Shea, under pressure from West Ham teenager Divin Mubama, levelled it before Soucek volleyed home a second in the first of seven minutes added on.
It was cruel on Burnley, who had largely contained a West Ham side devoid of inspiration without the injured Jarrod Bowen and Michail Antonio, but just when their fans thought they could celebrate a first home league win since May, it all fell apart at the death.
A side that broke records on their way to the Championship crown last term are now making too much unwanted history, with this loss seeing them match Newport's 53-year-old record of starting a league campaign with seven home defeats.
Burnley narrowly shaded a fairly dismal first half, but ended it frustrated after Luca Koleosho's penalty appeals were waved away six minutes before the break.
The teenager ran into the box and tumbled over the dangling leg of Vladimir Coufal but referee Sam Barratt, perfectly positioned, pointed for a goal-kick, deeming that Koleosho had run into the Czech defender, a view upheld by VAR Craig Pawson.
Koleosho and Burnley would get their penalty just two minutes into the second half. The Italy youth international appeared to have hit a dead end as he faced four West Ham players but - as he tried to turn away - he was caught on the heel by Mohammed Kudus and this time Barratt pointed to the spot.
Rodriguez had to hold his nerve through a VAR check but then fired his penalty under the dive of Alphonse Areola for his first goal of the season.
West Ham were forced to wake from their slumbers as the game finally came to life.
O'Shea blocked Soucek's shot after a free-kick from deep, then Sander Berge got in the way of James Ward-Prowse's shot following a long throw-in. Another set-piece came to Lucas Paqueta, but his powerful volley was still rising as it sailed over.
Burnley had chances to score what would surely have been a decisive second. Zeki Amdouni won possession on the right and charged into the box, forcing Areola into a sharp save at his near post.
Substitute Aaron Ramsey then went close to making an instant impact in the 73rd minute, springing forward down the right side and cutting in towards goal, only to send his shot over.
West Ham fans had been singing the name of Mubama before he replaced the largely-anonymous Danny Ings just after the hour, and the 19-year-old helped as West Ham turned up the wick late on.
Kurt Zouma blazed high and wide from Paqueta's cross before substitute Said Benrahma failed to get enough bend on a curling shot, but the pressure was building.
And it paid off when Kudus got to the byline and pulled the ball back towards Mubama, with the ball bouncing in off the unlucky O'Shea.
Burnley were still reeling from that when West Ham won it at the death, as Soucek met another Kudus cross with a superb volley.
