Substitute Greg Tansey produced a stunning 20-yard strike in the final minute of injury time to give Stockport a 2-1 win against 10-man Oxford.
The best chance of an otherwise forgettable first half came with three minutes to go when County's James Wallace fed David Poole and his chip flew inches wide.
Oxford went ahead four minutes after the break when Steve McLean put Tom Craddock through on goal and he powered the ball past 19-year-old Ian McLoughlin.
The Hatters sensed that they could get back into the game when Anthony Tonkin was sent off for a bad tackle on Poole in the 66th minute.
The equaliser came 10 minutes later when Tom Fisher spotted an unmarked Matt Paterson, who stroked the ball into an empty net after Oxford goalkeeper Ryan Clarke had been drawn out of position.
Oxford's rearguard action had looked to have paid dividends until Tansey's late intervention.
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