In just the second minute of the game, Morris scored his seventh goal for the club since joining in January, but elbowed goalkeeper Viktor Johansson in the process of heading in.
Rotherham missed a succession of chances to level, notably with Freddie Ladapo failing to tap in from just a few yards out and Brad Collins making a stunning save to deny Chieo Ogbene, and their survival chances are looking slimmer after a fourth consecutive defeat that leaves them four points from safety, albeit with two games in hand.
Story of the match
Barnsley were fresh from a convincing performance at Huddersfield Town three days earlier, and looked to crush another Yorkshire rival with the perfect start. The goal came after 90 seconds, but could have been even sooner had Johansson not been at full stretch to tip over Cauley Woodrow’s awkward half-volley into the ground that threatened to loop over him.
But from the resulting corner, Callum Styles crossed and Michal Helik headed towards goal, where Morris nipped ahead of Johansson to score. In heading in, however, his leading elbow smashed into the face of the goalkeeper, a clear foul that ended the Swede's afternoon with a suspected broken eye socket. It was bitterly ironic for Rotherham, whose midweek defeat to Middlesbrough owed much to a non-existent elbow that saw Matt Crooks dismissed.
When the match restarted, Paul Warne’s side rallied impressively to that latest blow to their survival hopes and would dominate. Chances were hard to come by at first against a team who haven't lost from a winning position all season, but after Ogbene volleyed a snapshot straight at Collins, two big ones came before the break.
First, a Jamie Lindsay chip over the defence sent Ladapo away, and he squared for strike partner Michael Smith at the far post. He ran onto it awkwardly though and needed a touch before he could shoot, by which time Callum Brittain had scampered across to be able to make a crucial block.
Another ball over the top caught Barnsley out a second time, Ladapo latching onto Lewis Wing’s pass this time and finding himself in on goal. His first touch was good but his second, aiming to poke in the equaliser, was blocked by the onrushing Collins.
After the break, only more agony would await. Ogbene had the first big opportunity with Collins standing up well to make another save, but Rotherham frustrations centred on a penalty not given for a possible foul on the forward by Michael Sollbauer as he ran in but honestly stayed on his feet.
Just moments later came a chance that even the player himself likely did not know how he missed. Smith played a cross which caught out the Barnsley defence completely, leaving Ladapo entirely free just a few yards out to tap in, yet he found his feet muddled and saw the ball remarkably go straight through them.
They could not have asked for a better chance, and it looked like they would not get another one. The hosts had been very quiet offensively ever since the goal, their only good attempt coming for Daryl Dike whose poke was deflected wide, but they were at least holding the fort at the other end and it was some time before Smith planted a header wide from a Wes Harding cross.
Another huge chance would come though, and come for Ogbene, who had been excellent throughout, with two minutes remaining. Ryan Giles’ cross was knocked down by Smith and Ogbene latched on to surely prod it in from point-blank range, yet Collins somehow got a hand to bat it away.
Barnsley had to cling on until the very end, with Helik and Mads Andersen denying substitutes Florian Jozefzoon and George Hirst respectively deep into injury time, but they kept a remarkable clean sheet intact for surely their most valuable victory of the season.
‘Really, really poor’ Reds
It is often said that a sign of a good team is being able to win when not at their best. If that is the case, this Barnsley side are very good indeed, because this display was among the worst seen in Valerien Ismael’s reign as head coach.
The boss admitted himself it was a “really, really poor performance”, lamenting a slow pace that is so unlike their usual intensity. Following a similar issue last weekend at Coventry City, which on that occasion did result in defeat, there is a small concern. If nothing else, it should keep them on their toes.
Their place in the play-offs should now be assured – Reading need to win their remaining three games while Barnsley would have to lose their final two – but this kind of offering will not do if they are to pull off the previously unthinkable.
Too many players are currently off the standards set throughout the season – Styles was hooked at half-time and Ismael admitted he could have brought off most of the team – and they cannot afford to be as strangely passive as they were in this game, the opposite of the style that has got them this far.
No luck for Millers
As if a schedule of 12 matches in five weeks was not bad enough for Rotherham, things could hardly have conspired against them any more cruelly this week. After a defeat to Middlesbrough which turned on a highly controversial red card when ahead, they went from bad luck to no luck at all here.
The contrast between that dismissal for Crooks – for nothing more than an accidental clash of heads, the elbow that led to the decision having missed entirely – and the nature of the decider in this match was not a satisfying one, as the actual real elbow of goalscorer Morris disfigured the eye of Johansson while heading in the game’s only goal.
Even Morris himself expected the whistle of referee Gavin Ward to sound, while Rotherham might also have had a penalty early in the second half, but ultimately the greatest disappointment should be that they played so well and created so many chances, only to fail to take them.
After surely the most gut-wrenching of four consecutive single-goal defeats, Warne acknowledged that “the most crucial part is putting the ball in the net and we didn’t do that”. But they did everything else superbly well and should not give up hope yet, even if it will feel like everything really is against them.
Man of the match - Brad Collins (Barnsley)
An brilliant performance from Barnsley's goalkeeper, who didn't put a foot wrong all match and made some exceptional saves.