Veteran striker Mark Robins snatched his first league goal for Wednesday but could not halt the slide as the Hillsborough side edged closer to the relegation zone following a 3-2 home defeat against Port Vale.
Chris Turner's side started the season as promotion favourites but a run of 11 league games without a win has seen them plummet.
Robins was signed from Rotherham to shake up Wednesday, who had failed to score in their last three home games, and had hit the net only three times in nine league games.
And when the 34-year-old ex-Manchester United front man hit the target in the 20th minute it seemed Wednesday were heading for a rare win.
But twice the Potteries side bounced back before snatching a winner with seconds to go.
Full-back Derek Geary pumped over a looping cross from the left, Paul Smith headed it back into the goalmouth and the little striker finished clinically from eight yards.
Port Vale were back on level terms just five minutes later, Littlejohn steaming in to latch onto a clearance and lash an unstoppable shot past David Lucas from 25 yards.
The Owls were back in control on the half hour after winning a free kick 30 yards from the Port Vale goal. Centre-back Graeme Lee tried his luck hammering in a right foot shot, the ball taking a deflection as it flashed past Jonathan Brain.
Guylain Ndumbu Nsungu hammered a stinging shot into the side netting before the Potteries side snatched a second goal in the 54th minute. The troublesome Littlejohn carved out the opening with a fierce shot which David Lucas could only push away and Billy Paynter added the finishing touch with Lucas stranded.
Robins had a chance 11 minutes from time running onto a Smith pass but he scooped it over the bar from 12 yards.
Substitute Steve Brooker had the last word beating Lucas with a low shot from 20 yards in the last minute.