Barnsley conceded a 98th-minute goal at lowly Blackpool after a poor second half performance in a 1-0 defeat on Saturday lunchtime.
The Reds dominated the ball in the first half and should have led but defended for most of the second half of a poor match played in constant rain.
Jordan Brown eventually found the net in the final seconds while the Reds did not have a shot on target all game.
They slipped down to fifth in the early League One table with 3pm games to come.
Barnsley kept the same team that beat Reading at home a week earlier, and the same bench.
The Reds began brightly and almost took the lead in the seventh minute when Caylan Vickers latched onto an Adam Phillips pass on the right of the box and crossed for David McGoldrick who shot wide of the bottom right corner from close range.
Barnsley thought they have could have had a penalty when Phillips appeared to be pulled down by Hayden Coulson in the box when trying to meet an Nathanael Ogbeta cross after a fine move down the left involving Luca Connell and McGoldrick.
Murphy Cooper then made a good save down to his left to keep out a low long-range effort by Scott Banks before, at the other end, Coulson twice gifted Davis Keillor-Dunn the ball just outside the Blackpool box but he shot over then wide from about 20 yards each time.
Barnsley had dominated possession in first half and played some attractive football but found themselves level at the break against a very defensive home side.
Blackpool started the second half much better, giving Barnsley far less time on the ball and attacking more often without creating many chances.
They almost took the lead just after the hour when Niall Ennis was put through but Jack Shepherd made a fine last-ditch tackle then was on the floor clutching his back during the goalmouth scramble before making another challenge on the ground to put the ball out for which the home fans wanted a penalty.
Albie Morgan volleyed straight at Cooper from outside the box then Dale Taylor was played clean through by his goalkeeper but took a heavy touch and Ogbeta cleared.
The hosts eventually won it in the eighth minute of stoppage time when, after Barnsley could not clear a set piece on the right, the ball was worked to Brown who found the bottom right corner from just outside the box.
Barnsley (4-2-3-1): Cooper; Watson, Shepherd, Earl, Ogbeta; Bland (Yoganathan 76mins), Connell; Vickers (Farrugia 65), Phillips, McGoldrick (Russell 90+2); Keillor-Dunn.
Unused: Flavell, de Gevigney, Rooney, Cleary.
Yellow cards: Bland.
Blackpool (4-4-2): Peacock-Farrell; Imray, Casey, Ihiekwe, Coulson; Bowler (Hamilton 76mins), Morgan, Honeyman (Brown 79), Banks (Hansson 81); Ennis, Fletcher (Taylor 76).
Unused: Ravizzoli, Horsfall, Evans.
Yellow cards: Morgan.
Goals: Brown 90+8.
