Three’s the magic number? It undoubtedly has been for Premier League champions Liverpool, whose three-card trick of Sadio Mane, Mo Salah and Roberto Firmino has been the bedrock of their spectacular title success.

However, the idiom is also posing a summer transfer dilemma for the club’s hierarchy as they decide whether to ‘stick’ with what they already have at the start of a new dynasty, or take a leaf out of Alex Ferguson’s book and strengthen when they are at their most powerful.

The temptation to maintain the status quo is a strong one. All three are approaching the peak of their careers — Mane and Firmino are 28 and Salah 27 — which goes some way to explaining the telepathy between them and the effortless rhythm of their inter-passing.

That relationship was underlined by the fourth goal in Wednesday’s 4-0 victory over Crystal Palace. One instant square pass from Firmino to Salah without even looking, a heads-up, slide rule pass inside the full-back from the Egyptian to Mane, and of course, the simple but ruthless finish from the goal scorer.

A scenario like that isn’t born in a moment of genius, it is crafted during years of working together. Remember, Firmino arrived at Anfield in 2015, Mane in 2016, and Salah in 2017. This symmetry is five years in the making.

Ferguson maintained United’s dynasty over 20 years by being willing to shake up his champions with a new signing. The club’s dominance began with the arrival of Eric Cantona and Roy Keane in 1992 but from them on, summer transfers were often one at a time and carefully selected in moments of success.

Cristiano Ronaldo, Carlos Tevez, Dimitar Berbatov, David de Gea, Andy Cole, Ole Gunnar Solskjaer, Teddy Sheringham and Jaap Stam all arrived after United had just won a Premier League title, and even in the Treble season of 1998-9, Ferguson spent big on Fabian Barthez and Mikael Silvestre as soon as the season was over.

The only times Ferguson didn’t spend were immediately after winning his very first title in 1993 and again in 2000 after his side won the title by 18 points. Whether there is anything there for Liverpool to learn is difficult to tell, but the underlying trend was that United spent money on big players, one at a time, when they were winning trophies and had power in the market.

Having won the Champions League last season and the Premier League this time, it’s hard to imagine a time when Anfield will be a more attractive proposition for the world’s best players if they want to follow that model — and there are signs they are tempted.

The fact that Liverpool were in the race for Leipzig striker Timo Werner before he joined rivals Chelsea suggests that even if he proved not to be the right player at the right price this time, they will not be afraid to upgrade their front three.

What Liverpool fans will be more nervous about is whether the club is willing to go a step further and offer one of their holy trinity as bait for a truly world class star, such as Kylian Mbappe, the subject of a recent swap rumour with Mane.

Looking at their Premier League rivals, it is becoming increasingly clear that it is an ask to expect the same trio to deliver over the course of a season without help from others — even though Mane, Firmino and Salah have managed to do so for the last two years.

At Manchester City, Pep Guardiola can currently juggle between Raheem Sterling, Sergio Aguero, Riyad Mahrez, Bernardo Silva, Gabriel Jesus and Leroy Sane; and the signing of Mahrez is an excellent example. He arrived in July 2018 for €65m just moments after City had won the title with a record 100 points and a 19-point gap between themselves and second-placed United.

Did they need him? Either way, he’s been a terrific signing.

At Chelsea next season, Frank Lampard will have Timo Werner to challenge Tammy Abraham and Olivier Giroud, flanked by Willian, Callum Hudson-Odoi and Christian Pulisic — and yet still they chase Kai Havertz, Said Benrahma, and Jadon Sancho to add to the mix.

If others are strengthening, then Liverpool will need to do so, too. History tells you they are not afraid to sell big names — going all the way back to Kevin Keegan, Ian Rush, Peter Beardsley, Michael Owen, Fernando Torres, Javier Mascherano, Luis Suarez, Philippe Coutinho and Xabi Alonso. Some of those departures have been painful, but others led to the emergence of new heroes in their place.

The ideal is for Liverpool’s front three to be the apex of their heavy metal football for years to come, creating a dynasty that would make the teams of the 1970s and 80s proud. But very few champions of the past have defended a title without adding quality when they were at their best.