Liverpool welcome Villarreal to Anfield on Wednesday and are heavy favourites in their Champions League semi-final tie.

Under Jurgen Klopp, the Reds have become one of the world's best teams. They have reached two Champions League finals, winning their sixth title in the competition in 2019, and followed that up with a maiden Premier League crown a year later. This season, their eyes are fixed firmly on an unprecedented quadruple – the EFL Cup is already theirs, they will face Chelsea in an FA Cup showdown next month and their race in the league with Manchester City is set to go to the wire.

Standing in Liverpool's way of a final against Manchester City or Real Madrid are, however, Unai Emery's Villarreal. While the Yellow Submarine will be considered underdogs, the reigning Europa League champions will be no pushovers.

Liverpool were frustrated for just over an hour by their relegation-threatened local rivals Everton in the Merseyside derby on Sunday, until Andy Robertson headed home and Divock Origi settled matters late on. They should be anticipating a similar test on Wednesday.

Yet whereas Everton are devoid of confidence or quality, Villarreal have both in abundance. They have already overcome European heavyweights in the form of Juventus and Bayern Munich, and will have home advantage in the second leg. They averaged just 35 per cent of possession across the two legs against the Bundesliga giants.

The last time these semi-finalists met was in the last four of the 2015-16 Europa League, and the two legs of this tie will come just a day under six years after each match in that previous fixture. Back in 2016, matters were rather different for Liverpool, who progressed 3-1 on aggregate, but went on to lose in the final to a Sevilla side coached by Emery.

It is fitting, then, that as Liverpool bid for European glory once more, a team that stood in the way of their first continental final under Klopp will try to prevent the Reds reaching a fourth with the German at the helm.

A remarkable turnaround

A quick glance at the team that started in the second leg of that 2016 tie, which Liverpool won 3-0 at Anfield, tells you the transformation that the Reds have gone through under Klopp has been dramatic.

Simon Mignolet started in goal, behind a back four of Nathaniel Clyne, the now-retired Kolo Toure, Dejan Lovren and Alberto Moreno (who might have been facing his former club for Villarreal if not for a serious knee injury sustained last month). Roberto Firmino and James Milner started, but they are the only two of that 18-strong squad that remain at Liverpool, and neither can be considered regular starters anymore.

Liverpool were convincing winners – racking up an xG of 3.8, producing 25 shots with 12 of those on target.

The team that take to the field on Wednesday will almost certainly feature a world-class goalkeeper in Alisson, one of Europe's best defenders in Virgil van Dijk, a Champions League-winning midfielder in Thiago Alcantara, two exceptional full-backs and, of course, a devilishly potent attacking trident, whichever three of Mohamed Salah, Sadio Mane, Diogo Jota or Luis Diaz line up. Firmino is unavailable.

Salah has returned to goalscoring form in timely fashion, after a relative dry spell. Only in 2017-18 (10) has he scored more Champions League goals in a single campaign than the eight he has netted this season, moving his tally for the club to 33. He is now just three behind both Didier Drogba and Sergio Aguero for the most goals scored in the competition for an English side.

For Klopp to take that Liverpool team back in 2015-16 to two finals (they lost on penalties in the EFL Cup to Manchester City that year) was, looking back, an extraordinary achievement, especially considering he only took over in October.

Since then, they have gone from strength to strength. In the Premier League, Klopp has won 162 of his 253 games (64 per cent), with his team scoring a remarkable 544 goals, and the German has averaged 2.15 points per game. He is building a true dynasty.

Emery to have his say?

"Unai's a world-class coach and is doing an incredible job," said Klopp in his pre-match news conference on Tuesday. And he is right, Emery – perhaps unfairly maligned during his stints at Arsenal and Paris Saint-Germain – has been brilliant for Villarreal.

He could well have left for cash-rich Newcastle United earlier this season but elected to stay put, and Villarreal are, at least in Europe, reaping the rewards. Their shoot-out success against Manchester United in last season's Europa League final represented Emery's fourth triumph in UEFA's second-tier tournament, and he also took Arsenal to the final in 2018-19, losing to Chelsea.

Villarreal are not flying quite as high in LaLiga, though surely that can be forgiven. They sit seventh, having won their last two games, and still have hope of qualifying for European competition through the league, too.

Emery has taken on Klopp five times as a coach, winning the first meeting – that Europa League final back in 2016.

Klopp claimed victory in two of the three Premier League encounters with the Spaniard's Arsenal, with those victories being 5-1 and 3-1 respectively. The other league match was drawn 1-1, while Liverpool also beat Arsenal on penalties in the 2019-20 EFL Cup after a wild 5-5 draw.

Emery can feel hard done by that he was not given more time at PSG. His win percentage of 76 was the best of any coach during the QSI era, putting him above the likes of Carlo Ancelotti (64) and Thomas Tuchel (75). He succeeded in 87 of his 114 matches in charge and claimed seven trophies. Only Laurent Blanc (11) has won more silverware at PSG since 2011, while Emery's team scored 2.7 goals per game, with just Tuchel managing to match that.

Yet Emery's ability to get a side competing way beyond their expected level is what he is renowned for. His run of three successive Europa League titles with Sevilla was extraordinary, and he seems to be in a similar position at Villarreal.

Having to rebuild his reputation slightly after his spell at Arsenal, Emery has won 51 of 104 matches in all competitions (49 per cent), with Villarreal scoring 188 goals and conceding 101, keeping 37 clean sheets.

Emery's win percentage has not been beaten by any other Villarreal coach to have taken charge of 100 matches, while in Gerard Moreno, who has directly contributed to 60 goals during Emery's tenure, the Spanish side have a brilliant striker to call on.

Liverpool have, in many ways, come full circle with this tie, but the Villarreal they will face on this occasion have improved just as much, in relative terms, as Klopp's team have. It is set to be a fascinating tussle.