James Henry scored a stoppage-time winner for Oxford United as they claimed a 2-1 win at Hillsborough after the Owls' Callum Paterson had cancelled out Cameron Brannagan's opener.
The manner of the defeat added more frustration for Sheffield Wednesday, who slumped to their third league loss of the season. They are already playing catch-up with the rest of the promotion contenders, sitting four points outside the play-offs after 10 games.
On the face of it, their defence looks solid and capable, with only league leaders Wigan Athletic conceding fewer goals this season.
However, Darren Moore' s side have let in almost half of their goals - 44 per cent to be exact - in the final 10 minutes of fixtures. Adding to that, a fifth of their goals conceded have come in the final 15 minutes of the first half.
After keeping four clean sheets at the beginning of the season, the Owls have now failed to keep their opponents scoreless in their last six League One outings.
"To lose the goal in the last minute is always disappointing," reflected manager Darren Moore.
"I said to the players that is probably one of the hardest ways to lose a game. When you concede in the last minute, it saps the energy away from you."
Moore is confident his players will learn from their mistakes as they prepare for another difficult home test against Bolton Wanderers on Saturday but not before they travel to Mansfield Town in the Football League Trophy this evening (7pm kick-off).
He added: "You learn from it. In terms of it being a three-game week and the physical demands on the players.
"To concede at the end, you don't see it coming as a manager but it has happened. It will be up to myself and the staff to see how that opportunity came to them."