Midson scored a stoppage-time winner to stun the Gulls, who had fought back from 3-1 down to equalise with 11 minutes remaining.
Goals from Tom Craddock and Midson put Oxford in command and Midson added a third after Elliot Benyon had pulled a goal back. But Torquay rallied, with Benyon and Billy Kee pegging Oxford back.
Chris Wilder's men were not to be denied, though, and Midson struck right at the death to seal all three points, much to the delight of the Oxford boss.
Buckle said: "We feel a touch deflated to be honest. We haven't had too many days at Plainmoor where we feel this deflated but we are after this game because I think we were by far the better team.
"Although we conceded four goals, we were the better team throughout and in the end I could only see one team that was going to win it. You have to give credit to Oxford for the breakaway goal (to make it 4-3) although we put so much into the game that the minimum we deserved to get out of it was a draw."