The Reds book another trip to Wembley after seeing off Derby at a rain-soaked Oakwell in the Carabao Cup.
Adam Hammill's first goal in over 10 months for the Reds came at a perfect time for Barnsley; his 89th minute wonder-strike sealed the Club's place in the third round of the Carabao Cup at the expense of Derby County.
Paul Heckingbottom made four changes to the side that drew 1-1 at Preston at the weekend with recalls for Ethan Pinnock, Harvey Barnes, Tom Bradshaw and George Moncur.
The Reds came quickly out of the blocks. Just three minutes played and it was lovely football down the left as Barnes played a one-two with Brad Potts before unleashing a rocket of a shot off the crossbar from all of 30 yards.
However, our visitors scored with their first meaningful attack. Johnny Russell was allowed too much room before curling home beyond Adam Davies from 10 yards out.
On 18 minutes Barnsley fired level...
A superb, in-swinging Ryan Hedges corner was thundered home by Adam Jackson, his header leaving Rams 'keeper Jonathan Mitchell no chance.
It was an entertaining first half with the Reds playing some fantastic, one-touch stuff, but again Derby broke on the counter to retake the lead.
Ikechi Anya got down the right hand side at pace before his inviting low cross to the far post found Mason Bennett sliding in to poke home for 2-1.
The Reds could have levelled on the stroke of half time but Potts' header from six yards out went just wide.
HALF TIME: Barnsley 1-2 Derby
In heavy rain now, the second half failed to get going until the Reds made two changes on the hour mark, with the introduction of Adam Hammill and Mamadou Thiam, and Barnsley going with two now in attack.
74 minutes in and Hecky's men equalised again...
Thiam's cushioned header was perfectly into the path of the fleet-footed Barnes, he fired in a low cross from the left and there was Bradshaw sliding in to make it 2-2.
It was all Barnsley now, and Hammill signalled his intention with a swerving free-kick that had Mitchell stationary but missed the target by an inch.
Cameron McGeehan his Reds debut with just two minutes remaining, and then with just one minute remaining, that man Hammill had the final say...
It was a lovely short corner that ended up with Hammill cutting onto his right foot from just outside the box and bending in a superb goal, giving Mitchell absolutely no chance.
So it's Wembley for Barnsley once more as Tottenham await next Tuesday night!
FULL TIME: Barnsley 3-2 Derby
Reds XI: Davies (GK); McCarthy, Jackson, Pinnock, Pearson; Williams, Potts (McGeehan '88), Moncur (Thiam '66); Hedges (Hammill '60), Bradshaw, Barnes.
Unused: Townsend (GK), Bird, Lindsay, Ugbo.