Barnsley have been relegated to League One after a 3-1 loss at Middlesbrough on Saturday.
Jean Yves M'voto gave the Reds the lead on 54 minutes but the hosts levelled seconds later then struck twice in the final minutes.
Danny Wilson's side needed a win to keep their fight going to the final day of the season but have gone down with a game to spare on the 17th anniversary of the day he got them promoted to the Premiership.
Wilson made three changes from the side that lost at Derby on Monday as Paddy McCourt, Lewin Nyatanga and Tomasz Cywka dropped out for Kelvin Etuhu, Ryan McLaughlin and Marcus Pedersen who all overcame injury.
Boro dominated the first half but were thwarted by the excellent Luke Steele who kept out a series of long-range shots.
The Reds took a shock lead nine minutes after the break when M'voto volleyed in Tom Kennedy's corner. But the lead last less than a minute as M'voto lost the ball to Lee Tomlin who fired in from the edge of the box.
Steele made another superb save from Tomlin before substitute Proschwitz volleyed wide when well-placed and M'voto headed over from another Kennedy corner.
Barnsley threw on Danny Rose and went with three up front but left themselves vulnerable at the back. Steele made a fine one-on-one save from Tomlin but then, when he did the same to Albert Adomah on 89 minutes, Danny Graham fired into the empty net. It was 3-1 in injury time when Tomlin got his second.