Three goals down, with no away goal to cushion any mistakes and Mohamed Salah, Roberto Firmino and Naby Keita out through injury, Liverpool’s chances of progressing to the final were slim at best.

Jurgen Klopp continued with his usual 4-3-3 formation, while Ernesto Valverde set up Barcelona in their usual 4-4-2/4-3-3 system, where Philippe Coutinho will push forward on the left but drop back alongside the midfield when defending and Arturo Vidal would tuck inside, leaving just Lionel Messi and Luis Suarez up front.

Desperately needing goals, Liverpool attacked and pressed high from the off. Divock Origi would block off the pass into Sergio Busquets while Xherdan Shaqiri and Sadio Mane blocked the passes into the full-backs, but if the ball was played short to Marc-Andre ter Stegen, Gerard Pique or Clement Lenglet, they would immediately press, quickly getting on top of them. Jordan Henderson and James Milner would push up behind them to stop Busquets or Ivan Rakitic from being able to turn on the ball and Trent Alexander-Arnold also came very high up the pitch to stop Jordi Alba from going free when Shaqiri moved towards Lenglet.

With this support, Liverpool’s forwards could confidently stay close to the opposition defenders, meaning they could put them under very early pressure, making it extremely difficult for Barcelona to pass out. Players synonymous with possession play like Busquets and Pique had to resort to clipping aimless long balls forward to stop Liverpool forwards pouncing on them.

Liverpool’s forwards block the passes into midfield

The ball is played short to Lenglet, who Shaqiri presses

He passes to Rakitic, who can’t turn out with Henderson behind

The ball goes back to the goalkeeper and Origi presses, with the short options marked

The ball goes long and Liverpool win the ball in the air

Alexander-Arnold pushing up on the right left a clear weak spot for Barcelona to try and take advantage of, but as they were struggling to pass the ball out they had no way of getting at it. Joel Matip would often get dragged out to the touchline to cover but he and Virgil van Dijk could comfortably win most headers in the air, which put an end to most Barcelona attacks. Barca would try to pass out under heavy pressure, be forced into going long to ensure they didn’t lose the ball near their box, Matip and Van Dijk would win the resulting aerial battle, then Liverpool regained possession.

Despite pushing Alexander-Arnold high into attack, Liverpool rarely looked exposed because Fabinho would drop back quickly, keeping a man advantage with the Brazilian, Matip, Van Dijk and Andy Robertson against generally just Luis Suarez, Lionel Messi and Coutinho if the former Liverpool man could get forward quick enough. The forwards would sometimes be able to hold the ball up, however Liverpool’s midfielders were generally far quicker at getting back to defend than Barcelona’s were in providing support, leaving the South Americans isolated.

Alexander-Arnold presses high

Barcelona attempt to exploit the space he leaves

Matip covers

Liverpool defenders outnumber Barcelona’s attackers

Barcelona’s front two were starved of supply but they were also ineffective defensively. They would lightly press Liverpool’s backline but not enough to really worry Liverpool’s centre-backs when they were in possession, enabling them to pick out passes from deep, and it also meant they weren’t in positions to block passes into midfield, with Fabinho often in acres of space.

This can be seen in Liverpool’s opening goal, where Matip picks up the ball in space and strides forward, before hitting a pass forward in an attempt to exploit Alba’s slow retreat into defence. He misplaces the pass but Alba’s header is poor and Mane, who had kept in position to put Lenglet under pressure, picks it up, slipping through the supporting Henderson, whose shot is rebounded into Origi to finish.

Matip has the ball in space

He strides forward and picks out a pass

Alba heads the ball back with Mane in a position to press

Mane picks up the ball

He slips through Henderson and Origi scores the rebound

The goal came at the perfect time for Liverpool. Although they continued to press, it was impossible for them to keep up such a high intensity for long, sprinting at 100% for every challenge (although no one seemed to tell Henderson this). Getting the early goal made the possibility of a comeback more likely and it meant that Barcelona didn’t get the mental boost of weathering Liverpool’s early storm. With Liverpool’s intensity dipping, the away side found it easier to keep hold of the ball and managed to create a few chances attacking down the left, although Alisson was superb in stopping them.

Liverpool still threatened too. Mane was trying to isolate Sergi Roberto on the flank, while Henderson would constantly bomb forward to join the attack. The captain’s tireless running was key to Liverpool’s success, adding an extra man to the forward line that enabled them to overload Barcelona’s backline.

An injury to Robertson saw him replaced by Georginio Wijnaldum at half-time, with Milner moving to left-back. Liverpool now had both Henderson and Wijnaldum bursting forward into the box, while Barcelona dropped off to protect their lead.

Within ten minutes, they had lost it. First Alexander-Arnold pounced on Alba in the final third and crossed into the path of the onrushing Wijnaldum to finish, then two minutes later Liverpool again won the ball in Barcelona’s half and, after one attack was repelled, Shaqiri got the space to cross for Wijnaldum to head home.

Valverde receives a lot of criticism yet it’s difficult to feel sympathy for him after this. He tried the same thing last season in Rome, trying to sit on his lead rather than add to it, and it failed spectacularly then. Barcelona aren’t really good enough defensively to simply sit back so the starting gameplan inevitably backfires, and when they need to get back into the game, they have surrendered so much momentum to the opposition that they can’t take back control. To make the mistake once is understandable, but to not to have learned from it is difficult to forgive.

Liverpool slowed down after going level, however Barcelona still couldn’t muster any reply – their passing not really going anywhere. Liverpool attacked down the flanks, with Shaqiri drifting wide on both sides to help double up with the full-backs.

One of the crosses that came from these attacks was deflected out for a corner and Alexander-Arnold, thinking quickly, played in Origi while Barcelona’s defenders were standing around with their backs to play. It’s not something you notice at the time, but rewatching the game it really stands out how lazy Barca are at set-pieces: they take an age to get prepared and when the ball is sent in many of them are stood around flat-footed with their hands on their hips. It’s something that Liverpool’s analysts had apparently noticed and, although it’s obviously a freak goal, it seems an obvious exploit with the benefit of hindsight.

Barcelona still couldn’t muster any response so Liverpool progress to the final in Madrid.