Across the 43-year history of their rivalry, Barcelona have never knocked Liverpool out of Europe, never defeated the Reds at the Camp Nou. Four home matches: two defeats, two draws, one solitary goal scored -- 12 years ago, by Deco. It's an angry blemish scarring an otherwise superb European record from a club that, like Liverpool, is pursuing its sixth Champions League trophy.

And the harsh truth, amid the champagne and backslapping of their La Liga title win on Saturday, is that if Barcelona perform against Jurgen Klopp's team this week like they did in beating Levante 1-0, then both those bleak records are guaranteed to continue. Their bid for a third Treble, when no other club has more than one, will be in tatters.

Does that sound a little ungracious given that for Barcelona's squad, staff and fans, this is a time of momentous achievement? Eight domestic titles in 11 seasons -- particularly, played in a league in which the quality is enormously high, in which it's proven that any team, however humble, can beat any other, and that is populated by serial UEFA trophy winners such as Real Madrid, Atletico Madrid and Sevilla -- is awesome.

However, facts must be faced. I'm stating the same truth that Ernesto Valverde, Gerard Pique, Luis Suarez & Co. will be digesting and trying to avoid at all costs.

What happened on Saturday, while Paco Lopez's Levante played absolutely superbly, going toe to toe with a squad that was assembled for hundreds of times the cost and is paid hundreds of millions more, was precisely what Lionel Messi has recently warned against. Barca's genius stepped off the pitch seconds after the final whistle against Manchester United in the quarterfinal and shrugged off praise from his interviewer so that he could go straight to the nub of the matter.

The gist of his message was: They have spoken among themselves about not playing as sloppily as they did in the first 10 minutes against United. They need to not repeat this again because a bad spell of eight or nine minutes in the Champions League and you're out.

The thrashings at the hands of Paris Saint-Germain, Juventus and Roma in recent seasons were the stimulus for his critical message. United, a team in stasis, had been dealt with, but no such advantageous circumstances lay ahead in the semifinal. Liverpool are better, faster, stronger and more confident.

It's worth going back to Messi's words because, against Levante, Barcelona were wasteful, slow and lacking intensity -- and that's before their level dropped.

Putting it politely, Liverpool's scouts must have left the Camp Nou licking their lips in anticipation. Klopp's players -- or at least those who weren't spending Saturday praying that Burnley would do them a favour against Manchester City -- would have been forgiven for messaging their agents to book flights and hotel rooms in Madrid, where the final will be held, for family and friends.

Lionel Messi's Barcelona will need to improve against Liverpool. David S. Bustamante/Soccrates/Getty Images

One reason for writing so scathingly about Barcelona's weekend performance is the clash against Klopp's red machine already felt like Superman meeting kryptonite for the first time.

In case you're not familiar with the 81-year-old extraterrestrial, he went by the name Clark Kent and has made millions for DC Comics and Hollywood filmmakers. He left mortals standing, but kryptonite mysteriously weakened him -- just as Liverpool's pressing, athleticism, high-tempo passing, three-man front line and height at set pieces can potentially do to Barcelona.

Indeed, just in case you've forgotten modern football history, never mind Superhero antecedents, it's not just PSG, Juve and Roma who are our reference points.

It's true Barcelona's home record could make the Camp Nou seem like an unassailable citadel. No team in Europe has an equivalent record of 31 home games in UEFA competition without defeat.

Liverpool, as powerful as they are and as much as the two rivals' states at present makes them feel like favourites, face a club that has won 28 and drawn three in the past six years, scoring 91 while conceding just 15 times. Pretty remarkable.

However, Barcelona's lone conquerors in that span were Jupp Heynckes' Bayern Munich. They were not identical to this Liverpool team, but not far off it: high tempo, physical, confident and wholly aware of where Barca's Achilles heel was in 2013.

It's coincidental that one of the jokers in Jurgen Klopp's pack, capable of springing surprises on unwary opponents and a different kind of footballer from those around him at Anfield, is Xherdan Shaqiri. He played for Bayern in that aggregate 7-0 semifinal rout.

If Klopp quizzes his Swiss international, Shaqiri will surely tell him that the 2013 version of Barcelona had also run away with their league title, but that they hated being harassed at high tempo, weren't at their athletic peak, were capable of being bullied, were vulnerable at set plays and needed to be overwhelmed.

I'd estimate Klopp's sermon to his players this week has been almost identical in content and tone to the one delivered by Heynckes. Bayern then, like Liverpool now, played 4-3-3, darting in behind the normally foraging Barca full-backs. The Catalans then, like Saturday at least, weren't at their peak of energy and stamina.

A year after Bayern thrashed Tito Vilanova's Barcelona 7-0 on aggregate, Xavi told me, vehemently, that the fundamental difference between the sides was that he and his teammates were exhausted and not at their physical best, and the Bavarians were absolutely flying in terms of pace, stamina and freshness. I was doubtful; the problems appeared to run more deeply. But it was only two seasons later that a buzzing Barca squad, not heavily changed but much more energetic after Luis Enrique had heavily rotated their first XI for months, pretty clinically dispatched Pep Guardiola's Bayern side in what was an epic Champions League semifinal en route to Barcelona's second Treble.

This lesson seems to be the key. If Barca are fresh, rather than frazzled, it's Liverpool who are underdogs. Otherwise, it's vice-versa. While Valverde has undoubtedly reduced the minutes of his vital, slightly more senior squad members, has it been sufficient?

If Messi is to fulfill his promise to bring the European Cup back to the Camp Nou, then there needs to be a massive leap forward in intensity, pace of passing, attention to detail, pressing and finishing.

Liverpool, judging by their domestic and European form, are coming to a boil. Barcelona, if you inserted a thermometer, would show a tepid temperature.

What Barcelona have achieved in winning the title both early and by a decent margin, while making this European semifinal plus reaching the Copa del Rey final, is exceedingly special. So few clubs have won Trebles because it's unbelievably difficult; there will be days when you win by luck, thanks to referees' blunders or, well, when you don't really know how you've got through.

So if you take a close look at Barca's recent level of performance -- away to United, at home to Atletico, in drawing 0-0 against Huesca, shipping four against Villarreal, ambling around against Real Sociedad and conceding sufficient chances to lose against Levante -- then the conclusion is that any team in this situation would be counted as distant second favourites to eliminate a phenomenon like Liverpool.

However, what's special about Messi, Pique, Suarez, Jordi Alba, Ivan Rakitic, Marc-Andre ter Stegen, Sergio Busquets isn't just their talent, it's their mentality.

They know that leaving massive gaps between the lines like they did against Levante, being robbed of the ball, giving it away lackadaisically, getting jittery and allowing the importance of the occasion to gnaw away at their intensity and excellence, well, that will end their European season. Goodbye, Wanda Metropolitano on June 1. Goodbye, Treble.

The thing about Superman is that he always found a way not to let the kryptonite finish him off -- by hook or by crook, his cape would always flutter, he'd soar above his apparently dominant rivals, his superpowers would always save the day.

Barcelona's task between now and Wednesday is to refocus, to accept that mental sharpness, intensity, concentration and experience must rouse in them a 180-degree transformation from the error-strewn, sloppy, below-par 90 minutes that won them the Spanish title to one of the performances of their entire lives against a Liverpool side who arrive at the Camp Nou, whether they admit it or not, expecting to win.