O'Connor arrived on an emergency loan from Birmingham City.
Barnsley boss Mark Robins said: "Garry was the catalyst and it was a great debut.
"It's something he'll remember and something the supporters will remember.
"He's with us for a month but it's something we'll be looking to do something more with. Birmingham might want him back after that game so I hope people don't write too many nice things about him!
"It was a great finish from him, straight into the corner. He's capable of doing it. It was pleasing for me how he ran at defenders. I've told the players that while we've got him, watch him.
"How he moves, the way he closes people down, you can learn plenty from him."