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If you were to slam your head against a brick wall for long enough, eventually it might just crumble. This is of course something best left to professionals at demolition jobs. Liverpool may yet have proven themselves to be that, not just in this competition but every one in which they played.

Certainly, there were moments when you felt that consistently testing the structural integrity of Unai Emery's battlements might leave Liverpool with a few sore heads (catch all the Champions League action on Paramount+). Though after given that an eventual breakthrough came, their fans certainly might have a few come Thursday morning as they celebrate another stride towards immortality for Jurgen Klopp's side.

There is no point acting like the quadruple is not an extremely live prospect a month and a day out from the Champions League final. Liverpool seem bound for Paris, having steadily but inevitably ground Villarreal into the Anfield turf.

It was never going to be easy, and for a moment early in the second half, just as Fabinho goal celebrations were cut short for a Virgil van Dijk offside, you might just have convinced yourself that the rub of the green was going to favor the side bedecked in yellow. Pau Torres, Geronimo Rulli and company delivered a masterclass in defensive football and precious little else. Unfortunately for Emery and company, they would eventually run into a harsh reminder that when you pack your penalty area and instruct your defenders to throw themselves at anything that moves, they might just send the ball flying in very much the opposite direction to that which they were intending.

You could not fault Pervis Estupian for his commitment in charging out to Jordan Henderson as the Liverpool captain shaped to cross. He did everything you could ask, he had even put his arms behind his back to mitigate against any risk of a penalty. The cross was only ever going to hit his left boot, it was just that on this occasion it rolled up his leg and high towards the Anfield Road end, looping agonizingly over a flapping Geronimo Rulli.

Villarreal were shell-shocked. If they were going to be undone, it would have taken a moment of magic from one of Liverpool's array of attacking talent surely? Not this fluke. That was still to come though. Moments later the yellow shirts sagged off Salah just for a moment, catching their breath while his back was to goal. In a flash he was facing them, drawing their attention as Sadio Mane darted in behind, the run timed to perfection. Through Raul Albiol's legs went the pass; Rulli could never have gotten out quick enough to block the shot.

Villarreal's reward for 50-plus minutes of obduracy and defensive excellence is now a two goal lead to overhaul at El Madrigal next week. It felt at once both the inevitable outcome for a team that took just one shot and a cruel endpoint to a run through Europe in which they have proven that such an approach can topple clubs with pedigree and firepower, both sporting and financial, that vastly eclipses this provincial Spanish city with a population that couldn't fill this stadium.  

For much of this match Liverpool could steal the ball back as high up the pitch as they might like, pushing their center backs right up to the final third, but they would still run into the same eight, nine or 10-strong defensive line. Any gaps to exploit between the defensive line were purely theoretical, nowhere near sizeable enough to fit a professional athlete in them.

That came at a cost with Villarreal scarcely offering any threat on the counter. Once or twice Arnaut Danjuma might hopefully chase a ball in behind only to find himself tasked with beating Liverpool's defense on his own. Giovani Lo Celso hooked a long Dani Parejo pass into the stands, it was to be the only shot Villarreal had until the game was long gone, when substitute Boulaye Dia rolled the ball to Alisson as if he were apologetically trying to involve him in the game. 

Liverpool would end with 20 of them, each of them requiring grade A quality in the build up, a first timed cross by Trent Alexander-Arnold on the volley here, a raking long drive from Thiago there. That ultimately is where Villarreal's plan fell down. It was going to take something remarkable to puncture this defense. But you never doubted that Liverpool would deliver it, even if it came with a helping hand from their opponents.