League One side Coventry City came from behind to beat Barnsley 2-1 and progress to the fourth round of the FA Cup at the expense of their Championship opponents.
It was Coventry who had the game's first clear-cut chance, as Leon Clarke forced Luke Steele into a good save in the 18th minute, but just a minute later the home side took the lead.
Jean-Yves M'voto flighted a ball over the Coventry defence and O'Brien kept his composure to dink it over the onrushing Joe Murphy to put Barnsley 1-0 ahead.
Tomasz Cywka then forced Murphy into a save with a well-struck free kick from 30 yards before the Polish striker rattled the post with a curling effort.
O'Brien and Cywka combined well after the break, but the latter couldn't connect with the cross properly and his weak header bobbled wide, while at the other end Denzel Slager, who was making his Coventry debut, forced Steele into a low save.
Cywka then fired over the bar when put through one-on-one, while David Perkins forced Murphy into a sprawling save.
Clarke then struck the crossbar, but with 13 minutes remaining Franck Moussa lashed the ball into the top corner to bring his side back on level terms.
Both teams pushed for a winner in an end-to-end final 10 minutes, but it was Clarke who put the visitors into the fourth round with a composed finish in the 89th minute.
