The result moved the Reds off the bottom of the table and cut the gap between them and safety by a point to five as fellow strugglers Charlton, Stoke and Wigan also won.
The game was not a classic but the hosts were the more positive and creative team throughout so deserved to win.
Clarke Oduor came into the side for Luke Thomas in the only change from the 3-0 win at Fulham a week earlier. Oduor played at left wing-back in a 3-4-1-2 with Kilian Ludewig the other wing-back while Jordan Williams was on the left of the three centre-backs.
The first half was a fairly dull affair, with both sides cancelling each other out in the same formation although the Reds were slightly the more lively and positive as they had the majority of the attacks and shots - mainly from long-range.
Both Alex Mowatt and Conor Chaplin had early shots from just outside the area which whistled narrowly wide of the bottom right corner then Cauley Woodrow fired straight at goalkeeper Aynsley Pears from even further out. At the other end, ex-Red Ashley Fletcher sent a header well wide before Ludewig volleyed straight at Pears from a very tight angle then Woodrow put a 25-yard effort well over.
Conor Chaplin almost opened the scoring just before the break, with the best chance of the half, but his flicked shot from a low left-wing cross by Oduor was straight at Pears.
At the start of the second half, Middlesbrough’s Lewis Wing sent a 25-yard free-kick wide of the bottom right corner. At the other end, Mowatt blasted over the bar from just outside the box then Woodrow and Oduor fired off target from slightly further out.
Woodrow then shot straight at the goalkeeper from 20 yards in the 70th minute, but the breakthrough came soon afterwards. Mowatt’s cross from the left was headed down at the back post by Jacob Brown to Chaplin whose first shot from eight yards out crashed against the crossbar before he fired in the rebound for his tenth league goal of the season.
Woodrow fired over from just inside the penalty area then Fletcher headed an injury-time free-kick over the bar from close range.
Barnsley (3-4-1-2): Collins; Sollbauer, Halme, J Williams; Ludewig, Mowatt, Bahre (Ritzmaier 88mins), Oduor, Woodrow; Brown, Chaplin (Thomas 82). Unused: Walton, B Williams, Dougall, Schmidt, Simoes, Ritzmaier. Yellow cards: Woodrow, Bahre. Goals: Chaplin 72.
Middlesbrough (3-4-1-2): Pearson; Shotton, Moukoudi, Friend; Howson, Saville (McNair 80mins, Wing, Johnson; Morrison (Coulson 79); Fletcher, Assombalonga Unused: Mejias, Clayton, Tavernier, Nmecha, Gestede.
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