If you needed the definition of a lightning start, Atletico Madrid’s rampaging counter-attackers were on hand to help you out in the first leg of their Copa del Rey semi-final with Barcelona.

Diego Simeone was wheeling down the sidelines twice before half-time as his Atletico side raced into a 4-0 lead at the break — after Antoine Griezmann, Ademola Lookman and Julian Alvarez added to the Eric Garcia own goal that put the home side ahead.

That was a calamitous moment for Barca’s back line, one where Joan Garcia had to take the blame. He failed to control a simple backpass from his namesake, the ball rolling under his foot and into an empty net, despite the goalkeeper’s frantic attempts to save the situation.

According to Catalan radio station RAC1, the last time Barcelona trailed a team by four goals at half-time was almost 73 years ago — in a La Liga match against Real Madrid on October 25, 1953 (which ended 5-0).

Barcelona suffered a damaging 4-1 defeat at Sevilla in La Liga back in October, where the risky nature of their high defensive line was similarly exposed.

This one, coming just a few weeks before the Champions League last 16, where they could face Paris Saint-Germain, will certainly be a concern — and to make matters worse, Eric Garcia was sent off with five minutes to play.

The second leg will be played on Tuesday, March 3, at Barcelona’s Camp Nou, at 8pm UK, 3pm ET.

Here, The Athletic’s Pol Ballus and Dermot Corrigan take us through the talking points.

Just how good were Atletico?

Simeone’s side were really up for this, bursting with athleticism and enthusiasm from kick off. Alvarez and Giuliano Simeone — the manager’s 23-year-old son — both had chances inside the first few minutes.

Barca then gave them a helping hand with Garcia’s howler, but Atletico kept their foot on the throttle and played some of the best football you are likely to see this season. Their second goal was made of real technical and tactical quality — as well as physical dominance.

Goalkeeper Juan Musso caught a corner and sent an accurate kick 60 yards to Lookman’s feet. Instead of sprinting for goal, the January signing from Atalanta calmly played it back to Alvarez, whose cross-field pass sent Nahuel Molina clear on the other side. Griezmann supplied the very calm finish through Jules Kounde’s legs and just inside the far post.

Simeone’s selections were all working — the hard-running Molina at right-back and intelligent Griezmann in an attacking midfield role especially. Meanwhile, Guiliano and Lookman looked like the ideal wide players to keep sprinting in behind Barca’s shambolic high defensive line.

The away side were rocking, and the waves of Atletico attacks kept coming. Griezmann and Alvarez missed clear chances to score before goal three came from another flowing move that cut Barca completely apart, as Griezmann, Giuliano and Alvarez combined to set up Lookman for a cool finish. Coach Simeone set off running down the line, shaking his fists and roaring in celebration.

And it just kept happening — just before half-time, Molina once again got clear down the right, his excellent curling cross found Lookman, who teed up Alvarez to thump in number four.

This was now an amazing scoreline, but Atletico had been so superior they arguably deserved to be even further in front. Only 45 minutes had been played of a two-legged semi-final, but Atletico’s players (and fans) could be forgiven for thinking they were already into the final.

Atletico have just won one Copa del Rey during Simeone’s 15 years as manager, back in 2013. They appeared in control early in last year’s semi-final against Barcelona, too, going 2-0 up after just six minutes, but the Catalans fought back to win 5-4 on aggregate.

Surely this time Atletico are heading to another final, in which they will likely be favourites for a first trophy of any kind since their La Liga crown in 2020-21. In the other semi-final first leg, Real Sociedad won 1-0 at Athletic Club on Wednesday.

Dermot Corrigan

And how bad were Barca?

Hansi Flick’s Barcelona have never looked as helpless as they did in this game.

Concerns over the high line have been there on many occasions since the German took over, but no team has dismantled the Catalans like Simeone’s Atletico did on Thursday night.

Marc Casado might take a big part of the blame. The 22-year-old midfielder was Flick’s surprise choice in the line-up, and ended up being replaced by Robert Lewandowski after 36 minutes, with Atletico already 3-0 up. Barca’s faults, however, went far beyond him.

Atletico were simply in full control of the scene in midfield and found a way to break Flick’s high line by quick switches of play and through balls. Barca were just chasing shadows.

A horrendous start to the match did not do the away side any favours. Joan Garcia failed to control an easy backpass from Eric Garcia to concede the opening goal. The Metropolitano crowd erupted and it helped the hosts take over the game. It soon turned into an Atletico feast.

Joan Garcia tries to scramble back and stop the opening goal (Angel Martinez/Getty Images)

Flick surely missed Raphinha and Pedri, arguably his most trusted performers on the pitch, who were out of the game through injury. But there has been a trend this season with Barcelona and slow starts. The defensive system has been less reliable than last term, after letting Inigo Martinez go last summer. Flick has struggled to find a consistent centre-back partnership, and injuries and bad runs of form from certain players have done the rest.

If you’re not on point, Barcelona’s daring high line risks becoming a liability. When you add to the mix an opposition that knows how to exploit it, this is what you get.

Pol Ballus

Why did that VAR check take so long?

Barca began the second half on the front foot, with Atletico looking a bit more apprehensive, and after 51 minutes it looked like Barca had got a foothold back into the tie when Pau Cubarsi knocked home from eight yards.

Inside the stadium, there did not seem to be any problem with the goal, and players from both sides turned to restart the game without much debate as the customary VAR check began.

Replays also appeared to show no problem with the goal. Lewandowski got a touch to Fermin Lopez’s shot before the ball dropped to Cubarsi to finish, but no visiting player looked offside when Lopez had struck his shot.

The VAR check dragged on and on… and on. Atletico fans began to get restless, while down on the pitch, the players who had initially looked to argue their case with referee Juan Martinez Munuera realised they needed to keep warm (it was 10:20pm on a chilly Madrid night).

Eventually, after almost seven minutes’ wait, Martinez Munuera signalled that an offside had been found by VAR official Pablo Gonzalez Fuertes. The decision appeared to be that when Lewandowski touched the ball, Cubarsi’s left foot was a millimetre or so ahead of both the ball and Atletico defender Ruggeri’s left foot.

After the match, the Spanish football federation’s technical refereeing committee said the delay was due to a fault in their semi-automated offside system, caused by a “high density of players”, which meant the offside lines had to be manually calculated in a slower process.

The long wait allowed Atletico to regroup and regain their composure, while Barca appeared deflated at missing out on an opportunity to get back into the match.

With five minutes left came another VAR talking point. Ferran Torres’ pass put Eric Garcia in trouble, and when Alex Baena got to the ball first, Garcia followed through and made contact with the Atletico midfielder.

A yellow card was shown to the Barca defender, but replays showed that Baena would have been clear in on goal, and suggested Garcia kicked him hard on the shins.

Atletico’s players, fans and coach Simeone all roared for a stronger punishment. Martinez Munuera was called to have a look at the pitchside screen, and the decision was changed to a red card. Barca did not like this VAR decision either — although it was definitely made more quickly than the disallowed goal.

Dermot Corrigan

What did Flick say?

“In the first 45 minutes we got a good lesson,” Flick said in his post-match press conference. “The distances were too long between the lines. We did not press how we wanted. What I can say is that there is a second game and we will fight for that.

“I am proud of my team. Maybe not today for the first 45 minutes, but yes for the whole season. We have had a lot of injuries, problems… and we adapted. This is a heavy loss, but I am proud of my team. We need to accept this lesson and make things better. When you see Atletico players they have more will and hunger. I want to see that too. We also have a young team, but that’s no excuse.”

What next for Atletico Madrid?

Sunday, February 15: Rayo Vallecano (away), La Liga, 3.15pm UK, 10.15am ET

What next for Barcelona?

Monday, February 16: Girona (away), La Liga, 8pm UK, 3pm ET