Jon-Paul Pittman came off the bench to fire Oxford to a first win in five matches in an action-packed 2-1 win over Northampton at the Kassam Stadium.
Pittman joined the action as a second-half substitute and fired in the winner 11 minutes from time, driving into the net from 12 yards from Peter Leven's pass.
That was just three minutes after the in-form Cobblers had equalised through their own super-sub Clive Platt. James Constable fired the U's in front after 14 minutes from Alfie Potter's low right-wing cross.
Oxford assistant boss Mickey Lewis said: "JP's come on and looked really lively. He has that ability to change a game.
"We need to get a bit more out of him, but he was terrific. We hit the woodwork twice right at the end on Tuesday at Barnet and we hit the woodwork twice again here, so I think we deserved a bit of fortune. That's if it was offside.
"And I don't want to sound like Arsene Wenger, but I honestly didn't see it properly, so I can't really judge."
Northampton boss Aidy Boothroyd said: "We're disappointed with the result but I've got to give credit to the opposition as they came at us strongly.
"I've also got to give my players for the way they came back."
Boothroyd had the added disappointment of seeing defender Clarke Carlisle sent off in the last minute for a second yellow card.
And he said: "We've been on a good run ourselves, so this is a bit of a reality check for us."