The match appeared to be heading for a stalemate until substitute Adrian Lopez poked home two minutes into injury time.

It was less dramatic than Dejan Lovren's header against Borussia Dortmund two weeks previously - Jurgen Klopp's side still have the home leg to come - but frustrating nonetheless as they had appeared to have ground out a draw.

Going to the El Madrigal, where the hosts have now won all seven Europa League ties this season and are unbeaten in the competition since matchday one on September 17, was always going to be tough - but the Reds seemed to have done the hard work until a momentary lapse in concentration cost them.

Daniel Sturridge was on the bench again for Liverpool - a pattern repeated over four European matches now - despite his four goals in the last five games. Roberto Firmino was given the role as a nominal centre-forward.

While the Brazil international did a lot of the hard yards, pressing from the front as per his manager's instructions, he could offer neither the pace nor precision Sturridge has.

Klopp had urged his players not to waste that dramatic win over his former side two weeks ago and Joe Allen, on his first European start since November 26 and only his fourth in the competition this season, almost got them off to a flier.

Arriving into the penalty area at speed in the fifth minute he could only direct Adam Lallana's cross straight at Sergio Assenjo when a shot a yard either side of goalkeeper would have produced the breakthrough.

Unforgivable to lose a goal on the counter attack in last minute of a European away game. But still fancy us to go through.

— Jamie Carragher (@Carra23) April 28, 2016

Without the focal point of Divock Origi, who injured ankle ligaments a week ago in the Merseyside derby but fortunately does not require surgery and could make a return before the end of the season, Liverpool were aimless in the final third.

Too often crosses were swung in at no one in particular, giving centre-backs Eric Bailly and Victor Ruiz an easy ride.

As a result Villarreal had the better chances with former Tottenham striker Roberto Soldado off-target with two shots at either end of the half, while Simon Mignolet got down well to parry Tomas Pina's low effort.

Villarreal right-back Mario Gaspar also had efforts snuffed out by Kolo Toure, continuing in central defence with Mamadou Sakho now officially suspended by UEFA for a failed drugs test - and Lovren.

The ineffectual Philippe Coutinho - reportedly being watched by Barcelona scouts - was replaced by winger Jordon Ibe at the break after feeling unwell but within 40 seconds of the restart Cedric Bakambu headed against the post from Jonathan dos Santos' corner.

Firmino, having kept himself onside, responded midway through the half with a shot which Asenjo tipped onto the upright - but that was as close as the visitors came.

Mignolet came to their rescue three minutes from time when Bakambu seized on Ibe's mistake while charging full-back Alberto Moreno ignored the unmarked winger from a quick counter-attack and instead fired into the side-netting.

But in added time substitute Lopez slid home after Denis Suarez had outpaced Toure.

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