The Reds will now face Walsall in the first-leg of the play-off semi-finals next Saturday evening after the Saddlers hammered Port Vale to confirm their third-placed finish.
Barnsley were simply irresistable. They came from behind to comprehensively thump the hosts, who saw Chris McCann sent off late on.
The Latics continued with their promotion celebrations of course, but for Reds’ caretaker boss Paul Hckingbottom, now it’s time for preparing his players once again following an afternoon he will clearly cherish for quite some time.
Heckingbottom said: “In terms of performances since I’ve been in charge that has to be right up there. It was certainly my favourite.
“It wasn’t just just the result and the occasion, it was the way the lads carried instructions out as an all-round thing.
“We have to take confidence from that now. Wigan showed why they’ve been crowned champions early on but as soon as we got back to our game-plan, we got the rewards. Once we got in front we knew we’d be able to sit back a little with two banks of four and be in control when we had the ball.
“It’s just a massive confidence-booster for us going into next weekend now.
“It’ll be tough as Walsall enjoyed a big win and played well themselves, but as long as we prepare right, hopefully we ca get back to Wembley for the play-off final.”
Heckingbottomfielded an unchanged team for the third consecutive time. Fit again was o the bench, but the line-up looked capable of spoiling Wigan’s title-winning party.
The Latics recalled goalkeeper Lee Nicholls, defender Jason Peace and front-man Yanic Wildschut. Former Reds midfielder David Perkins started with Reece Wabara a sub.
Wigan opened the scoring after 10 minutes with the first chance. Yanic Wildschut did well to beat Josh Scowen down the left before crossing and ass Alfie Mawson tried and failed to make a clearance just six yards from goal, newly-crowned League One player-of-the-month Will Grigg lashed past Adam Davies clinically from close range.
The Reds were up against it, with McCann twice going close to increasing the lead.
The Reds were in need of a bit of inspiration, and many hopes will have been pinned on wing star Adam Hammill.
He jinked his way past Donervon Daniels in the 26th minute, only to fire harmlessly straight at ‘keeper Lee Nicholls.
The Reds got their equaliser just past the half-hour mark. Ashley Fletcher was tripped in the box by Stephen Warnock and referee Mr Harrington pointed to the spot.
Coolness personified, Sam Winnall stepped up to comfortably beat Nicholls, and it was game back on.
Unbelievably, Winnall did the business again a minute before the break. The first-half turnaround was completed when he tucked home a rebound sharply after Nicholls could only parry Lloyd Isgrove’s shot. It was the former Scunthorpe man’s 21st league goal of a the campaign.
Into the second period Wigan sub Ryan Colclough went close, before at the other end, Hammill’s acrobatic volley was smartly saved by Nicholls.
The visitors surged into a 3-1 lead in the 56th minute, and again Fletcher was the provider. The Manchester United loanee teed up Conor Hourihane to joyfully fire home from 18 yards via the slightest of deflections.
And Barnsley were home and dry Josh Brownhill made it 4-1 in the 74th minute, curling home a breath-taking free-kick from 25 yards to spark wild celebrations among the 4,770-strong travelling army.
Hammill went closest to a fifth goal for the Reds late in the game, but it mattered not, Heckingbottom’s charges continue to chase that Championship dream next weekend.
WIGAN (4-3-3: Nicholls 6; Daniels 5 (Wabara 46, 6), Morgan 5, Pearce 7, Warnock 4; Power 7, Perkins 7, McCann 4; Jacobs 7 (Vukic 68, 6), Grigg 6, Wildschut 6 (Colclough 46, 6). Subs not used: Jaaskelainen, Morsy, McAleny, Barnett.
BOOKED: Perkins (34).
SENT OFF: McCann (90).
BARNSLEY (4-4-2): Davies 7; Scowen 7, Mawson 8, Roberts 8, G Williams 7; Isgrove 7 (McCourt 78, 5), Brownhill 8, Hourihane 8, Hammill 8; Winnall 8 (Toney 85, 6), Fletcher 8 (Chapman 78, 6). Subs not used: White, Townsend, Nyatanga, Tuton.
BOOKED: Hammill (90).
REF: Tony Harrington (Cleveland).
Super Barnsley will head into the Sky Bet League One play-offs bouncing with confidence after they demolished champions Wigan to book their dream sixth-place finish.