Millwall came from behind to thrash 10-man Barnsley at The Den and book their place in the Fourth Round of the FA Cup after a stunning second-half display.

Ben Thompson marked his first start since August by scoring his first goal of the season, either side of two Aiden O’Brien goals. Fred Onyedinma added a fourth for The Lions after a stunning Steve Morison flick, all after Brad Pott’s had given The Tykes an early lead.

Joe Williams was sent-off for Barnsley’s seven minutes into the second period after a poorly timed tackle on Jed Wallace and the visitors never recovered.

Neil Harris made six changes from Monday’s defeat at Carrow Road, as David Martin, Conor McLaughlin, Tony Craig, Thompson, Wallace and O’Brien all came into the starting-eleven.

The Tykes had won their previous five against Millwall, including their last two at The Den, one of which was the 3-1 success here in September, but that run came to an end against a rampant Lions side.

The hosts made a bright start as Craig fired over after Shaun Hutchinson’s knock-down early on, but with just ten minutes on the clock, the visitors took the lead. Adam Hammill’s cross was half-cleared, and Potts was there to slam home from six-yards.

Onyedinma had a chance to bring The Lions level, but his shot was blocked after Steve Morison’s flick-on put him through on goal. He then had an even better chance minutes later, but couldn’t get a proper connection on Wallace’s cross.

A half-empty Den crowd were becoming increasingly frustrated with their side as they were giving the ball away far too easily. Craig the guilty party on this occasion as he tried to find O’Brien, but gave it straight to a Barnsley player and they broke away.

The home side continued to create chance, but there finishing was letting them down, until O’Brien swept home his first goal since September. A superb tackle from Craig, found Wallace, who crossed for O’Brien to sweep home via Davies’ legs. It was no less that Millwall deserved.

O’Brien went close to helping himself to his second of the afternoon, but Dimitri Cavare cleared the danger after he had flicked the ball over Davies.

Harris’ side should have gone into the break ahead, but Wallace somehow prodded wide at the far-post after O’Brien send over a lovely cross.

The Lions didn’t have to wait long to turn things around, though, as just three minutes into the second-half, Thompson met O’Brien’s low cross to slot home.

Barnsley’s afternoon went from bad to worse on 52 minutes as Williams was sent off for a horrific tackle on Jed Wallace. The Lions players and fans were furious and referee Darren Bond needed no second invitations to give him his marching orders.

It didn’t take Millwall long to make numerical advantage count as O’Brien made it 3-1, curling home from 20-yards after Wallace’ shot had been blocked.

The Lions were in the no mood to let-up and added a fourth on 61 minutes. Morison skilfully found Onyedinma with a beautiful flick, before he controlled and curled home into the far-corner with his left-foot.