A quick look at the La Liga table offers two reasons for Arsenal to be brimming with confidence going into Wednesday night’s Champions League semi-final first leg against Atletico Madrid.

One is the 25-point gap between Diego Simeone’s side and leaders Barcelona, and the other is the defensive record of the once tightest team in Europe. Gone are the days when 1-0 was by far and away the most common scoreline in Simeone’s now 14-and-a-half-year tenure.

The line of six he strung across the back against Chelsea in two European knockout ties of February and March 2021 is a distant memory. He employed that tactic in the home leg, which his team lost 1-0, and then appeared not to abandon it until the second half of the second leg, which ended in a 2-0 defeat.

Why has Simeone shrugged off the ultra-defensive philosophy that made him one of Europe's most successful – and highest-paid – coaches? That won him and Atletico two league titles, two Europa Leagues and two Champions League runners-up medals?

The fact that its powers had waned is one reason, but another is that Simeone came under pressure from the people who run the club to shake off the shackles. There has been a flair transplant at Atletico, with the black-suited curmudgeon Simeone having so many stylish players at his disposal that the team have morphed into a far more expansive and entertaining unit.

Atletico bought Portuguese playmaker Joao Felix for Simeone to build a side around in 2019, but he was able to resist doing so because the £110million signing from Benfica never came close to living up to the hype around his arrival. 

But it was Simeone himself who wanted the club to spend £80m to sign Julian Alvarez from Manchester City in 2024 and with new majority owners Apollo Sports Capital demanding the club thrill a global fanbase, not just pander to the local nostalgia for Atletico to be the gritty Spanish capital underdogs, the fantasy football has flowed.

The downside has been some calamitous defensive displays and regular chaotic goal-fests, where once there was dour and dogged defending.

Atletico have conceded seven more than Barca in La Liga and six more than second-placed Real Madrid. Even surprise package Getafe have conceded three fewer than Simeone's team. 

In the Champions League group phase, Atletico conceded the most goals of any team that finished in the top 16 (15 in eight games). Their semi-final opponents Arsenal, who have taken up the mantle as European football's standard-bearers for defensive solidity, have been particularly miserly in this competition, keeping eight clean sheets in 12 matches.

And when the Spanish league, the Spanish Cup or the Champions League has gone goal-crazy this season, Atletico have usually been involved – for better or worse. They've conceded three or more goals on nine occasions in all competitions, including against relegation strugglers Elche last midweek.

In the Champions League knockout rounds they conceded four over two legs against Bruges and five over two legs against one of the worst Tottenham teams in living memory. Johan Cruyff’s famous mantra ‘I’d rather win 5-4 than 1-0' would have appalled peak Simeone in 2014 and 2021 when his team won La Liga, conceding 26 and 25 goals respectively. With five games still to play this season, it’s already 37.

Keeper Jan Oblak has dominated Spain’s coveted ‘Zamora’ prize. The award, named after former Barcelona and Real Madrid goalkeeper Ricardo Zamora, and given to the keeper with the best goals-conceded-per-game ratio, has been his for a record six times.

But this year he is fourth in the rankings and there have even been doubts over whether he should reclaim his starting place after a recent rib injury meant Argentine No2 Juan Musso was given a run of games, in which he impressed.

All of this comes with a major caveat: the defensive frailties have arguably made Atletico a better cup side. They reached the Copa del Rey final, losing it on penalties to Real Sociedad earlier this month, and now they are 180 minutes from another shot at lifting the trophy they have so nearly won three times in their history.

A Luis Aragones goal had put them 1-0 up in extra-time against Bayern Munich in 1974 but in the last seconds of the game a pot-shot from Hans-Georg Schwarzenbeck forced a replay which Atletico lost 4-0. 

Then came the twin horrors of defeats by neighbours Real Madrid, first in Lisbon in 2014 when Sergio Ramos’ 94th-minute equaliser took the cup from Simeone’s hands as Real Madrid ran riot in extra-time.

And then in Milan two seasons later, with Antoine Griezmann missing a penalty in normal time that might have spared Simeone the agony of a 1-1 score after 90 minutes, and defeat in the shootout that followed extra-time.

Griezmann, 35, is in his last weeks as an Atletico Madrid player. He will join Orlando City this summer after 10 seasons at the club across two spells, with his 212 goals making him their all-time top goalscorer. 

No one has revelled in Simeone’s new-found expressionism more than the Frenchman, who for years suffered silently filling-in as a wide midfielder in a line of four protecting the five-man defence.

Now, with Barcelona and Arsenal target Alvarez just ahead of him, and Simeone's son Giuliano and the in-form Ademola Lookman out wide, Griezmann is at the heart of a deadly attacking quartet.

Simeone’s Atletico have never been so threatening. But as Arsenal won’t need reminding after their 4-0 win over them in the league phase, they have also never defended so badly.