Liverpool and Tottenham recovered from seemingly impossible situations to show that, in the Champions League, anything is possible these days

Yes, yes, very good, but does the Champions League have any other tricks? It has become like Jed Mercurio killing off major characters long before the end of a series: the overturning of what would once have seemed impregnable leads is beginning to lose its shock value.

It is astonishing how perspectives change. When Manchester United won 3-1 at Paris Saint-Germain in the last 16, it seemed a comeback for the ages, the sort of performance and result that would never be forgotten. Now, if it exists in the collective memory at all, it will be as another example of PSG’s flakiness or the culmination of that strange two-month period when it seemed Ole Gunnar Solskjær might be able to turn United around essentially by sticking on a late-90s mixtape in the dressing room.

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As comebacks go, United in Paris feels distinctly quotidian alongside what Liverpool did to Barcelona and then, even more dramatically, what Tottenham did at Ajax. Liverpool on Tuesday night was the third three-goal lead overturned from one leg of a Champions League knockout tie to the next since the beginning of 2017. There have been a further three two-goal leads overturned in that time: that total of six is as many as in the previous 31 years of the competition.

So why? What is going on?

Quick guide Tottenham v Liverpool: the Champions League final Show Hide The venue: Estadio Metropolitano, Madrid (Saturday 1 June, 8pm) A new venue for the Champions League showpiece and it hosts the first final since 2015 not to feature at least one Madrid team. Atlético spent around £200m overhauling the 20,000 capacity Estadio La Peineta in the Las Rojas neighbourhood before moving in September 2017. It will hold 63,500 for the final, with 17,000 tickets allocated to each club. Demolition of Atlético’s former home, the Vicente Calderón stadium, began in February. This season's meetings Tottenham 1-2 Liverpool (15 Sept, Wembley) Liverpool made it five wins out of five at the start of the season with a deserved victory. Goals came from Georginio Wijnaldum and Roberto Firmino either side of the break before Erik Lamela’s consolation in stoppage time. Liverpool 2-1 Tottenham (31 March, Anfield) Last-gasp drama as the match headed for a draw: Toby Alderweireld prodded the ball into his own net to hand Liverpool a vital three points after Lucas Moura’s second-half effort had cancelled out Firmino’s early strike. The history It will be the second all-English final after Manchester United beat Chelsea on penalties in Moscow 11 years ago. Liverpool have won the European Cup five times: 1977, 1978, 1981, 1984 and most recently under Rafael Benítez in 2005. A sixth win would lift them to third behind Real Madrid (13 wins) and Milan (seven). Tottenham have reached their first European Cup final in their fifth campaign. They won the Cup Winners’ Cup in 1963 and Uefa Cup in 1972 and 1984. Routes to the final Tottenham Group B Inter (a) L 2-1, Barcelona (h) L 2-4, PSV (a) D 2-2, PSV (h) W2-1, Inter (h) W 1-0, Barcelona (a) D 1-1 Qualified: Barcelona 14pts, Tottenham 8pts Last 16 Borussia Dortmund (h) W3-0, (a) D1-1 Quarter-final Man City (h) W 1-0, (a) L 4-3 Semi-final Ajax (h) L 0-1, (a) W 3-2 Liverpool Group C PSG (h) W 3-2, Napoli (a) L 1-0, Red Star (h) W 4-0, Red Star (a) L 2-0, PSG (a) L 2-1, Napoli (h) W 1-0 Qualified: PSG 9pts, Liverpool 9pts Last 16 Bayern Munich (h) D 0-0, (a) W 1-3 Quarter-final Porto (h) W 2-0, (a) W 1-4 Semi-final Barcelona (a) L 3-0, (h) W 4-0 Compiled by Benjy Nurick

Photograph: Robbie Jay Barratt - AMA/Getty Images Europe

There are structural reasons. The introduction of the backpass law in 1992, the continuing liberalisation of offside and the crackdown on intimidatory tackling have all made it harder for teams to kill a game. Whatever else Fifa has done, the programme it introduced after the 1990 World Cup to make the game more open has been a raging success.

Football is a more attacking game now than it has been in half a century. Since 2008-09 the knockout stage of the Champions League has produced an average of more than three goals per game in all but one season; in the 14 years before that – that is, when a quarter-final phase was introduced after the groups – it produced more than three goals per game only twice.

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Obviously, the more goals there are, the greater potential there is for big swings. 2008-09, it may be noted, was Pep Guardiola’s first in management. The change of mentality he brought about among the elite, the realisation that it was possible almost to treat an 11-a-side game as you would five-a-side, has had a profound impact on how the game is played.

Possession has become far more important than position, and that perhaps makes a team more vulnerable if things begin to go wrong: the traditional defensive bulwarks are not necessarily there any more.

A manager such as Jürgen Klopp meanwhile, who is so adept at whipping his players to a frenzy, takes an enormous risk. His whole approach, tactical and emotional, can produce great highs but also great lows; it is as though he is operating on a higher amplitude than everybody else. That is how his side could beat City three times last season, but also lose 5-0 to them – it is no coincidence that he had already pulled off one three-goal European comeback in his time as Liverpool manager, against Borussia Dortmund in the Europa League quarter-final in 2016.

Yet the change is not matched in domestic football: over the past decade in the big four leagues there has only been one season that yielded more than three goals per game, in the Bundesliga in 2013-14.

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That suggests a certain decadence at work, that the superclubs, used to dominating domestically, have forgotten how to defend, that they spend so much time attacking they lack organisation and discipline, perhaps even the mettle, to stage a successful rearguard.

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That explains why the environment is conducive to sudden lurches of momentum; it does not explain why now. The answer to that is probably simply that once comebacks start happening they begin to seem possible: the chasing side realises a lead is not unassailable while the side with the advantage begins to tighten up.

It is like the four-minute mile. The athletics world was gripped in the early 1950s by the race to become the first to break the mark – it had been a target consciously chased since at least 1886 – yet once Roger Bannister had finally dipped under four minutes, 65 years ago this week, he was followed by a rush of others: John Landy broke his world record 46 days later and a couple of weeks after that Bannister and Landy both went under four minutes in the same race. By the time half a century had gone by, more than 1,000 others had done it: the barrier was psychological as much as it was physical.

Play Video 1:45 Emotional Lucas Moura reacts to replay of his match-winning goal against Ajax – video

A small-scale footballing example of that came in the Uefa Cup in 2005-06 when Middlesbrough, having overcome a three-goal deficit to beat Basel in the quarter-final did so again in the semi-final against Steaua. Almost as soon as Massimo Maccarone began the second comeback, it had a sense of inevitability: everybody at the Riverside had seen that film before.

At half-time in Amsterdam Tottenham, needing three goals in the second half, cannot but have thought of Liverpool scoring three in a half against Barcelona the night before. This was doable – and that sense conditioned the response both of players and fans. What is believable becomes achievable.