League One Barnsley knocked Middlesbrough out in the first round of the Carabao Cup for the second successive season thanks to Josh Benson's injury-time goal.
With the game seemingly destined for penalties, the former Burnley man slammed home a rebound after his initial shot had been saved by Boro goalkeeper Liam Roberts.
Chris Wilder's men enjoyed the majority of possession but failed to really trouble Barnsley goalkeeper Jack Walton.
Boro, who signed United States international striker Matthew Hoppe earlier on Wednesday, have now failed to win any of their three matches so far this campaign.