IT was throwback Thursday at Old Trafford. 

Here were Manchester United defeating world-class opposition, with a glorious comeback, in front of an ecstatic Theatre of Dreams.

And now they head to Wembley in search of a first trophy in six years – with four pieces of silverware still to play for in all this season.

Goals from the Brazilian duo of Fred and Antony saw United recover from a half-time deficit to dispatch the Spanish league leaders on a night to remember.

Erik ten Hag, who has transformed an ailing monolith with his quiet authority over the last six months, had enjoyed dinner with Sir Alex Ferguson earlier in the week.

And this was a hedonistic reminder of Fergie times, a retro night which made you recognise, after years of slumber, what this once-mighty club is all about.

Barcelona had bossed the first half and led through a Robert Lewandowski but after Ten Hag replaced the lumbering Wout Weghorst with Antony at the break, United attacked with purpose and passion and fully deserved their place in the Europa League’s last 16.

Next the Red Devils head to Wembley to face Newcastle in Sunday’s Carabao Cup Final, where they will be to end the club’s longest trophy drought in four decades.

In terms of the recent form and the history of both clubs, this was a world-class fixture, out of context as a Europa League play-off tie.

These two have contested three major finals, and a fair few more epic encounters down the years – now both are resurgent after a period in the doldrums.

The pre-match excitement was palpable – the primal roar and the acrid stench of pyrotechnics at kick-off time spoke of past glories.

Ten Hag made no attempt to rest first-teamers ahead of Wembley, it would have been ill-mannered in the extreme to disrespect guests of this calibre.

Barca’s wonderkids, Pedri and Gavi, were both injured but the runaway La Liga leaders still had ample star quality.

United began at a fair old pelt, former Real Madid man Casemiro – smelling the scent of Clasicos past – played a cute diagonal pass to send Fernandes clean through but Marc-Andre ter Stegen saved his angled shot with his legs.

After failing to make a difference in the Barca box, the United skipper managed to do so in his own penalty area.

It was a daft, needless spot-kick to concede – Raphael Varane had headed clear a cross and Alejandro Balde was moving away from goal, near the edge of the box, when Fernandes dragged him down.

It was soft but ref Clement Turpin was right to award it and, after a stuttering run-up, Lewandowski scored – David De Gea getting a hand to it but only able to help it into the net.

Barca were certainly proving themselves smarter at winning fouls and Ten Hag was becoming increasingly animated on the touchline.

United were struggling to make inroads, only a volleyed attempted cross from Fred worried Ter Stegen for a second but it landed on top of the goal net.

De Gea almost gifted Barca a second in first-half injury-time when he passed straight to Sergi Roberto but Casemiro staged an heroic resue act, with a tackle, then a block to deny Franck Kessie.

At half-time, Ten Hag sent on Antony in place of Wout Weghorst, moving Rashford into the centre.

And United were level within 75 seconds of the restart, Jadon Sancho feeding Fernandes who swept a pass to Fred, the Brazilian midfielder shinning his effort past Ter Stegen.

The din was deafening and there was an even louder roar soon after when Varane sent Antony galloping down the right but he was denied by an excellent sliding tackle from Andreas Christensen.

The tempo of United’s play and the volume of their supporters had been cranked up significantly and Barca, so assured in the first half, were visibly rocking.

Fernandes riled the visitors by drilling the ball into the body of a prone Frenkie De Jong – the man who refused to move to Old Trafford last summer.

The Portuguese was booked and the Stretford End saluted him.

The momentum has all been with United – their tackling, especially from Lisandro Martinez, was emphatic, their passing swift and purposeful.

But then De Jong curled in a centre and Jules Kounde’s header forced a gymnastic save from De Gea, tipping over the bar.

Ten Hag sent on his second peroxide blond winger, Alejandro Garnacho, joining Antony. As a gentleman it was a surprise the United boss hadn’t preferred them both in the first place.

Lewandowski crunched into Casemiro, both men needing treatment, Barca’s big Pole getting booked.

The winner arrived on 73 minutes and it owed a lot to a sensational back-heel from Luke Shaw, on the run, which prevented the ball going out for a goal-kick.

From there, Fernandes fed Garnacho, who had a shot blocked, as did Fred, before Antony side-footed a peachy effort inside the far corner.

Varane cleared off the line from Lewandowski deep in injury-time.

United deserved their win, though. Now they must drag their battered bodies south for a Cup final against a well-rested Newcastle.

But right now it feels as if Manchester United never know when they are beaten.

And there aren’t many more nostalgic feelings than that.