After bagging the goal that gave Irvine a winning start in his new job, Johnson – who celebrates goals by flapping his arms like wings – insisted that the Owls could still fly high enough to win promotion this season.
Irvine might have performed miracles on a shoestring budget at his former club Preston North End – leading the humble Lancashire club to the brink of the Premier League – but promotion this season? Surely you have got to be joking, Jermaine?
Maybe the Jamaican has not been looking too closely at the Championship table during the last few weeks and does not realise that the Owls are fighting to avoid the drop after going three months without a win.
Even this victory over local rivals Barnsley leaves the Owls a point adrift of safety in the relegation zone but Johnson is refusing to lower his sights.
With 22 games to play, the Owls would probably need to pick up around 17 wins to have a chance of getting in the top six. An impossible target? Not according to Johnson.
"Everyone believes that we can still climb out of the relegation zone and try to fight for a play-off spot," he said.
"That is certainly my aim. Everyone just needs to believe in themselves again and do their best."
Johnson thinks Irvine's appointment is a master-stroke by chairman Lee Strafford and cannot understand why the Scot was out of work considering his two-year record at Deepdale.
"To be honest, I never thought Preston would let him go but their loss is our gain and I am really pleased that he came to us because he is a good coach," he said.
Irvine has made it clear that survival is the Owls' only target this season with 53 points needed to avoid the drop.
Johnson was recalled as one of three changes to the side that had lost its last fixture two weeks ago in the FA Cup against Crystal Palace.
Predominantly employed as a winger, Johnson was asked to partner Marcus Tudgay in attack due to the absence of strikers Leon Clarke and Francis Jeffers with hamstring strains.
Defender Lewis Buxton and midfielder Michael Gray were also back in the side.
Barnsley manager Mark Robins was without influential midfielder Bobby Hassell due to a groin strain and Brazilian midfielder Anderson De Silva was dropped to the bench. Nathan Doyle returned to the line-up after completing a permanent move from Hull City, along with winger Adam Hammill.
The Owls took less than three minutes to go ahead as Tommy Spurr scored following a blunder by goalkeeper Luke Steele
Defending a corner, Steele attempted to punch the ball clear at his near post but knocked it down. Unable to retrieve the situation amid a crowd of legs, Steele was helpless as Spurr turned the ball home.
The Owls held the advantage for just four minutes before another goalkeeping error allowed Barnsley to equalise.
Lee Grant may have been linked with a possible move to Premier League Burnley following the appointment last week of former Owls manager Brian Laws but his failure to deal with a far-post cross from Emil Hallfredsson was anything but top quality.
Grant was caught in two minds as the ball sailed over his shoulder and into the net.
If that was an unfortunate slip, it was nothing compared to Darren Purse's howler soon after.
Centre-back Purse has been guilty of a string of mistakes since his summer arrival from Cardiff City and will not have impressed new manager Irvine with the attempted back-header that put Barnsley striker Daniel Bogdanovic through on goal just moments after the equaliser.
Fortunately for Purse, he was rescued by Grant.
Both sides showed the commitment that is needed in a high-octane local derby and the football was often fast flowing.
Barnsley conceded the second, and what proved to be the winner, in the 21st minute when Johnson slipped his marker on the edge of the area and volleyed past Steele.
But they were unlucky not to level again before the break when Stephen Foster's header was headed off the line by Darren Potter.
After a lengthy period of stalemate, Robins made a triple substitution in a bid to turn the game, sending on strikers Andy Gray and Iain Hume and the tricky Jamal Campbell-Ryce.
Hume was unlucky not to start after a good performance as substitute against Coventry and again showed his ability to spark things in attack.
Although Barnsley improved briefly, Johnson could have put the game beyond doubt with 12 minutes to go. The Owls winger delayed a shot with only Steele to beat, allowing Doyle to get back and challenge.
As Irvine led his players off at the final whistle, there was only one thing Owls supporters wanted to do; thank him for the result. Irvine warned that it was "only the start" of a difficult task.
"If we feel that is everything going to be okay now, we will end up having problems," he said. "We have set the benchmark now in terms of how we need to go about games and it us up to us to make sure we do not fall below those levels of commitment and determination and application."
Johnson's optimism is admirable – but he should also heed the words of his manager.
Barnsley: Steele; Shotton, Foster, Moore, Dickinson; Hammill, Colace, Doyle, Hallfredsson (Campbell-Ryce 65); Macken (Gray 65), Bogdanovic (Hume 65). Unused substitutes: Preece, Kozluk, Butterfield, Anderson.
Sheffield Wednesday: Grant; Buxton, Beevers, Purse, Spurr; Johnson (Sodje 87), Soares, Potter, O'Connor, Gray; Tudgay. Unused substitutes: McAllister, Esajas, Lekaj, Simek, Boden, Jameson.
Referee: A Penn (West Midlands).
Hero: Jermaine Johnson
Playing in attack rather than his preferred position on the wing, Johnson scored the winner for Wednesday and was a constant threat to the Barnsley rearguard.
Villain: Luke Steele
The Barnsley goalkeeper's form has dipped of late and he will reflect on both goals scored by the Owls knowing he could have done so much better.
16th minute: With the scores level at 1-1, Barnsley striker Daniel Bogdanovic wastes a golden opportunity to score.
Andy Penn: Held his nerve in a big-game atmosphere and was not swayed by the optimistic clamour for home penalties.
Great start for Owls' new manager Alan Irvine but a third consecutive defeat suggests Mark Robins' honeymoon period at Barnsley is over.
Barnsley v Leicester, January 26, Blackpool v Sheffield Weds, tomorrow.
Quote of the day
Did Sheffield Wednesday beat us or did we beat ourselves? I think it is the latter.
– Barnsley manager Mark Robins on their derby defeat.
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