The Reds went down to a 1-0 defeat in a match that, even at this stage of the campaign, had a must-not lose feel to it.
Former loanee Ashley Fletcher did the damage with the only goal of the game after the break as Boro took advantage of some poor defensive play by Dimitri Cavare.
The loss, the second new boss Gerhard Struber has suffered in two games, leaves the Tykes struggling to keep their heads above water in the Championship table as they are already eight points adrift of safety and in need of an SOS if they are to survive relegation.
This was no different to the majority of the Reds’ 17-game winless run. They competed well, against a side who had been in just as bad form, had chances to score, but were undone by a leaky backline.
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An even first half had ended goalless as both sides battled against the conditions, where the Riverside Stadium pitch had standing water on such was the deluge.
A brilliant goalline clearance by Ben Williams denied Britt Assombalonga while Mike Bahre and Cauley Woodrow were off target for the Reds.
The decisive moment in the game came with nine minutes of the second half gone as Cavare missed the opportunity to clear, allowing Marcus Tavernier to set up Fletcher, who delayed his finish to slam home.
Barnsley rarely looked like getting back into it and had it not been for goalkeeper Samuel Radlinger, this would have been a heavy defeat.
Middlesbrough: Pears, Howson, Ayala, Fry, Dijksteel (Bola 23), McNair (Clayton 78), Wing, Tavernier, Coulson, Assombalonga, Fletcher
Unused subs: Mejias, Wood-Gordon, O’Neill, Liddle Hackney
Barnsley: Radlinger, Cavare, Diaby, Andersen, B Williams, Bahre (McGeehan 69), Mowatt, Chaplin, Thomas (Schmidt 73), Brown, Woodrow
Unused subs: Collins, J Williams, Dougall, Sibick, Oduor,
Referee: Oliver Langford