Jamaica international Jamal Campbell-Ryce grabbed a stunning goal as struggling Barnsley chalked up their first league win at Hillsborough for 26 years.
Barnsley were still looking for their first win of the year after five straight defeats had sent them plunging towards the relegation zone.
The Oakwell side, who had not played for 17 days after having two matches postponed, started brightly against Wednesday, still reeling from their South Yorkshire derby defeat at Doncaster on Saturday.
Campbell-Ryce carved out an early chance, cutting inside from the left flank to fire in a low drive that was blocked by centre-back Lewis Buxton.
Wednesday, still harbouring ambitions of a top-six finish, found a gap in the Barnsley rearguard, Leon Clarke slipping the ball to Marcus Tudgay whose stinging right foot strike from 14 yards slammed against Hugo Colace as Barnsley broke quickly.
Bobby Hassell's long throw was hastily cleared to the waiting Colace 20 yards out but he mistimed his shot slicing the ball wide of keeper Lee Grant's right-hand post.
Wednesday escaped again, Campbell-Ryce's deep corner found Malta international Daniel Bogdanovic at the far post. He pumped the ball back into the goalmouth as centre-back Stephen Foster beat his marker only to head over the woodwork from eight yards.
Barnsley finally broke the deadlock in the 38th minute with a goal of real quality. Bogdanovic picked out Campbell-Ryce on the left flank and he showed quick feet to outwit James O'Connor as he rounded the midfielder to hammer his angled shot into the roof of the net from 14 yards.
Barnsley keeper Heinz Muller was quickly off his line to punch clear in a crowded goalmouth before Jermaine Johnson was foiled by full-back Hassell as he lined up a right-foot strike from the tightest of angles.
Wednesday almost snatched an equaliser in the 67th minute. Darren Potter's teasing corner was missed by Muller as full-back Marciano van Homoet headed clear from under the bar.
Seconds later Johnson cut in from left wing and his fierce angled drive was fisted out by Muller as the Sheffield side piled on the pressure.
Tudgay latched onto a loose clearance and his low shot on the turn was scooped up on the line by Muller before substitute Wade Small, on for Johnson, tried his luck with a long-range strike, the ball flashing the wrong side of the bar.
Potter caused problems as Wednesday chased the equaliser. His curling free-kick was met by centre-back Richard Wood whose header was snatched from under the bar by Muller before the Barnsley keeper performed more heroics stretching to push another Potter free-kick clear at the far post.