The centre-back, dubbed 'The Radiator' by sections of the Owls supporters has become an instant hit since his move from Plymouth earlier this month.
After an impressive debut in the FA Cup, keeping a clean sheet against Championship side Bristol City, the 22-year-old French-born defender capped an impressive home bow with his first Wednesday goal.
Yet for the first six minutes of an enthralling game against promotion rivals Charlton it seemed more like 'The leaky Radiator' as the shell-shocked Owls found themselves 2-0 down.
But the unflappable Johnson – who reminds fans of former Owls favourite Carlton Palmer, all legs and arms – helped lead Wednesday's recovery.
First he was hauled down for a 38th minute penalty. Although Tommy Miller was thwarted in his spot-kick by Charlton goalkeeper Rob Elliot, it at least perked up Wednesday.
And when Johnson headed home a 51st-minute equaliser – substitute Paul Heffernan had earlier reduced the deficit within a minute of his half-time introduction alongside the impressive Jermaine Johnson – the home fans had finally found a new hero.
But it was his defensive qualities which were just as impressive.
One particular crunching tackle midway through the second half was sublime, hunting down his opponent before a perfectly-timed tackle saw him emerge with the ball.
"Reda has had a fantastic start and everybody has taken to him," said Owls chief Alan Irvine. "I bumped into some Wednesday fans on the way back from Bristol and they were absolutely thrilled with him then. There are probably a lot more Wednesday fans more thrilled with him now.
"He's made a couple of mistakes, which we will talk to him about, and try to eradicate, but he is a young centre-back and will make mistakes. He's had a great start, the goal is an added bonus."
Wednesday had a terrible start to their first game at Hillsborough in over a month because of plumbing problems over Christmas. Scott Wagstaff poked the ball beyond Nicky Weaver before Darren Purse hacked down Joe Anyinsah to concede a needless penalty which Johnnie Jackson converted.
Miller then failed from the spot – the first penalty miss of his career – and a chorus of boos greeted the half-time whistle.
After a half-time dressing room rant from Irvine –- he accused some players of "hiding" in the first half – Wednesday came out looking a different team. And it was the double half-time substitution which created and converted the first goal.
Jermaine Johnson's cross found Heffernan who netted for his second successive home game after coming off the bench.
It was all square on 51 minutes when Chris Sedgwick picked out Reda Johnson for the equaliser.
The Owls dominated the second half and should have snatched a late winner, but Heffernan's header was tipped on to the inside of the post by Elliot and the ball was hacked away to safety.
Sheffield Wednesday: Weaver, Morrison, Purse, R Johnson, Jones, Sedgwick, O'Connor, Miller, Teale (J Johnson 46), Morrison, Mellor (Heffernan 46). Unused substitutes: Jameson, Spurr, Beevers, Palmer, Potter
Charlton Athletic: Elliot, Francis, Jackson, Semedo, Wagstaff, Racon (Ecclestone 69), Doherty, McCormack (Redid 84), Fry, Anyinsah (Sodje 61), Dailly. Unused substitutes: Worner, Abbott, Fortune, Jenkinson.
Referee: C Boyeson (East Yorkshire).
Man of the match: Reda Johnson.
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