In a Championship match generally lacking quality, Morris came off the bench to great effect with an excellent strike which went in off the post, his second goal in as many matches.
Captain Mowatt then rounded goalkeeper Thomas Kaminski in the final minute of normal time, which proved crucial when Adam Armstrong ran through and lobbed Brad Collins in added time.
While Barnsley can look up the table, the top six looks increasingly unlikely for Tony Mowbray’s Blackburn after a third successive defeat and another poor performance.
Story of the match
Neither side are renowned for easy-on-the-eye passing games, and it was an attritional contest. Barnsley, on the back of hugely impressive displays against Chelsea in the FA Cup and Brentford in the league, started the brighter with Conor Chaplin showing great technique to chest and volley from distance, Kaminski beating away, before Cauley Woodrow headed over a Callum Styles corner.
Blackburn looked to test the hosts with balls in behind the defence and twice came close, with Sam Gallagher failing to control an Elliott Bennett ball when he would have been in on goal, before strike partner Armstrong was beaten to the next by goalkeeper Collins.
Barnsley continued to probe at the other end with Romal Palmer volleying narrowly wide, before Kaminski was required to make a quick reaction save to keep out Victor Adeboyejo’s smash when the forward was smartly played in by Chaplin's quickly-taken free kick.
Their visitors finished the first half the better though, twice coming close to a breakthrough. Collins had to scramble a Stewart Downing corner off his line, with the midfielder returning the ball to the far post where Darragh Lenihan headed straight at the keeper. Bradley Dack then headed a Barry Douglas cross over, after good work down the left involving Armstrong.
Valerien Ismael had been an agitated spectator throughout the first half and by the 63rd minute the Barnsley head coach had used all five of his available substitutions, including an all-new front three, to try and shake things up.
Mowatt and Callum Brittain had efforts blocked as the changes took effect, while Gallagher’s tame header from a Lenihan square was the best Blackburn mustered before the game reached its closing stages, and the home side really gathered momentum.
Defenders Mads Andersen and Michal Helik both failed to take great headed chances, the former denied by Kaminski from a Mowatt free kick and the latter missing the target from an excellent Brittain cross. But it was substitute Morris who made the difference, receiving the ball from Mowatt more than 20 yards out, turning and composing himself before stroking a perfect shot past the motionless keeper and in off the post.
Blackburn still had almost 20 minutes to respond but they failed to pose any great threat, and a second goal always looked likelier to come for Barnsley. So it proved as Mowatt, moments after blasting one chance over the bar, sealed the three points by bursting through an all-at-sea defence from a Morris pass and rounding Kaminski to slot home.
That should have settled things, but it proved a crucial goal when one defensive switch-off allowed Armstrong to run onto Harvey Elliott's ball and score his 19th goal of the season in the 94th minute. One final flurry came but Blackburn's efforts were too late.
Reds have enough in reserve
Ismael’s main target in his first transfer window as Barnsley boss was adding quality and depth to the squad, especially in forward areas, and this match was a perfect justification of that approach as they found the strength from their bench to win the match having not been at their best.
Morris was the obvious standout substitute, coming on to score a brilliant goal to break the deadlock and adding an assist for Mowatt’s strike, as well as generally causing trouble on the left of the front three.
That the entire frontline was switched in a triple sub for the second match running shows not only that Ismael is using the availability of five substitutions to his advantage, but that there are a great volume of options in attack, helped by another January arrival in Daryl Dike, on loan from Orlando City, who also came on.
The depth extends to the defence as well, with Toby Sibbick impressing since being brought in from the cold by Ismael, while Jordan Williams played the entire second half as he continues his comeback from a spate of successive injuries. When their final January addition, centre-back Liam Kitching, finally recovers from injury to make his debut, they will have strong options across the whole pitch.
Rovers can wave away play-offs
These two sides were level on points coming into the match, and with a significant gap to close on the play-offs three points were critical. And while it would be too simplistic to say that the losers would be condemned to mid-table obscurity, the manner of this third consecutive defeat for Blackburn did nothing to suggest they have a fighting chance of making the top six.
They opted to counteract Barnsley’s defined style of play by matching their formation while playing long with the ball, both to be less susceptible to the press and to take advantage of their opponents’ weakness in behind. To a large extent it worked in frustrating the home side, but it ripped the creative heart right out of their own team.
The midfield was almost non-existent while the wing-backs, Douglas and Bennett, were less than comfortable in unfamiliar roles. That all left the three most advanced players, Dack, Armstrong and Gallagher, with little more than scraps to work with, and only in the fourth minute of added time did it come to anything.
While a team out of form and perhaps struggling in confidence, the way Mowbray chose to worry about the opposition at the near-total expense of his own side’s strengths was a surrender that only reinforced the view they are no longer in the play-off picture.
Man of the match: Alex Mowatt (Barnsley)
Barnsley’s skipper produced an all-action display, leading the attack from the centre of the park while providing constant bite to keep Blackburn quiet, and he fittingly rounded things off.