Ten-man Wednesday lost an amazing encounter at London Road, going down 5-3 against Peterborough United.
In what was an extremely open League 1 contest, the Owls took the lead three times in the first half.
Jermaine Johnson was first on target with a well-crafted goal inside five minutes. Craig Mackail-Smith levelled for the hosts but Gary Madine regained Wednesday's lead four minutes later.
George Boyd restored parity again for Darren Ferguson's men - that is before Chris Sedgwick struck low and hard beyond Peterborough keeper Joe Lewis in a pulsating first half.
But after the break Darren Potter saw red for a last-ditch challenge on Mackail-Smith and Posh immediately took advantage of the sending off as Boyd grabbed his second of the game five minutes later.
The home side flung men forward in search of a winning goal and duly found it through substitute Nathaniel Mendez-Laing near the death.
Posh grabbed a fifth when Nicky Weaver went up for a corner in the last minute but a quick counter saw Mackail-Smith run down the other end to finish into an empty net.
The Owls made five changes at London Road for the League 1 clash, with Lewis Buxton, Mark Reynolds, Sedgwick, Madine and Neil Mellor all started against the Posh.
It was a bright start from Wednesday, who were immediately on the front foot, winning a flurry of corners from which Madine and Mellor both went close.
Nicky Weaver had to stay alert at the other end, making a smart save from Peterborough captain Boyd but Wednesday promptly broke the deadlock with a swift attack.
Giles Coke found Jermaine Johnson in space out on the left and the lively winger beat two defenders inside the area and smashed past Posh keeper Joe Lewis to give the Owls an early advantage.
In what was a high-tempo start at London Road, the hosts went close to a leveller moments later, again through Boyd.
The striker took aim from 30 yards but Weaver did well to tip the ball round the post with an acrobatic dive to his left.
Jermaine Johnson was giving the home side a problem out wide on the left in the opening 15 minutes and almost created an opening for Mellor, delivering a dangerous low ball into the area but Lewis was equal to the striker's effort.
But the Posh were back level with their next attack. Lee Tomlin picked up a loose ball 30 yards from goal and blasted on target.
Weaver did well to keep out the first strike but Mackail-Smith was quick to react and put the rebound into the net.
The game was certainly not short of early action and Alan Irvine's men regained the lead almost instantly.
Coke, who was seeing a lot of the ball in the early exchanges, shot from outside the area and after the ball struck two Peterborough defenders, Madine finished clinically into the bottom corner.
But Posh then got themselves back on level terms just before the half-hour mark. Boyd made a quick break towards goal away from Reda Johnson and hammered a low strike which flew under Weaver.
Both sides looked dangerous going forward and more goals seemed inevitable as Mellor went close to regaining Wednesday's lead but saw his strike from close range trickle inches wide.
Incredibly, Wednesday took the lead for the third time in the half - this time through Sedgwick.
The midfielder intercepted a stray ball and played a clever one-two with Mellor before unleashing an unstoppable drive across the face of goal that struck the post on its way into the net.
Tomlin threatened another equaliser when he fired inches over the bar from 20 yards but Jermaine Johnson came within a whisker of making it 4-2 before half time.
Peterborough could not handle the Jamaican's pace and trickery as the winger thrashed another strike just wide of Lewis' left hand post.
The Owls were forced into a change at half time with Jermaine Johnson struggling to continue with Gary Teale coming on from the bench.
Coke went close minutes after the restart as the midfielder thumped a half volley into the side netting before Mellor tested Lewis with a thunderbolt strike from distance.
The second half started as the first concluded and both sides were threatening to add more goals.
But then the game took a sour turn for Wednesday when Darren Potter was issued with a straight red after 69 minutes.
Tomlin played a cutting through ball in towards Mackail-Smith and Potter's last ditch tackle brought down the striker down and referee Geoff Eltringham showed the midfielder a red card.
Boyd then struck again for Peterborough to level at 3-3 with 15 minutes left to go.
The home side had plenty of men in Wednesday's box and a cross into the box fell nicely into the feet of Boyd who got his toe to the ball to put beyond Weaver.
That goal had buoyed the home side who went in search of a winning goal and almost found it as Mackail-Smith fired a dangerous ball across the face of goal which Michael Morrison somehow managed to clear two yards out.
But with five minutes on the clock, the Owls could not hold out as Peterborough found a way through.
Substitute Mendez Laing raced in towards goal and saw his first shot blocked by Reda Johnson - which seemed destined to go well wide - but the striker poked home at the second attempt.
With the Owls reduced to ten men, Peterborough were taking the game to the visitors as Boyd almost scored his hat trick.
With time running out - Weaver went to join the attack from an Owls corner - but Peterborough were able to break quickly on the counter and Mackail-Smith ran down the other end to finish into an empty net to seal victory.
Peterborough: Lewis, Kennedy, Langmead, Lee, Wesolowski (Little 46), Boyd, Mackail-Smith, Rowe (McCann 62, Bennett, Whelpdale (Mendez-Laing 67), Tomlin
Unused substitutes: Jones, Frecklington, , Davies, Basey
Owls: Weaver, Buxton, M Morrison, R Johnson, Reynolds, J Johnson (Teale 46), Potter, Coke, Sedgwick (Jones 80), Madine, Mellor (O'Connor 72)
Unused substitutes: Jameson, Beevers, Heffernan, C Morrison