The first goal came from the left winger, the second from his right-sided counterpart. It felt typical. Such has been the way for Liverpool. It is partly because of how prolific Sadio Mane and Mohamed Salah are and partly because, given Jurgen Klopp’s idiosyncratic tactics, the nominal wide men are sufficiently narrow they can spend more time in the penalty box than on the touchline. Each outscores the supposed striker, Roberto Firmino, but as he drops in behind them, the front three is inverted, just like their relationship. The centre-forward, far from being the most selfish player, is the most selfless, the leader of their pressing. So far, so unconventional. Liverpool’s title challenge is propelled by the sides of the team. Andrew Robertson could become just the third defender to register 10 Premier League assists in a season. Trent Alexander-Arnold has seven. Klopp attributed the breakthrough in Sunday’s win against Chelsea to a half-time intervention to enable the right-sided trio of Alexander-Arnold, Jordan Henderson and Salah to combine differently. And yet it was notable that, unprompted, Klopp raised the influence of the spine of the side. He talked of them as a unit: Firmino, Fabinho and the centre-backs Joel Matip and Virgil van Dijk. He argued their defending against Eden Hazard and Jorginho was “the best I saw in my life.” The fifth component of the centre of the side, Alisson, contributed with a vital save from the Belgian. In an instant, Klopp, the tactical innovator, sounded a traditionalist. Established wisdom has it that you build around the spine of the side; the flanks are fripperies until the core is there. The scoring charts show an evolution with the rise of the potent winger, whether the Liverpool duo, Hazard or Raheem Sterling, but in a sense Klopp has followed a time-honoured approach with new sums of money. Matip is a free transfer, the fourth-choice centre-back who has risen to the challenge in recent months. Alisson, Van Dijk and Fabinho cost a combined £180 million (Dh866.1m). Brian Clough won the title in 1978 with Nottingham Forest after spending a then sizeable sum of £270,000 on Peter Shilton. Sir Alex Ferguson ended Manchester United’s long wait in Peter Schmeichel’s second season in goal. Whether or not Alisson deserves to be bracketed with them, he represents an enormous upgrade on Simon Mignolet; there is a school of thought that, in the corresponding fixture in 2014, after Steven Gerrard’s infamous slip, that Mignolet should still have saved Demba Ba’s shot. He did not. Van Dijk’s transformative effect is no secret. He has been the classy colossus, seemingly bigger, quicker and calmer than all-comers. He and Alisson made an immediate impression. Fabinho is the sleeper hit, not trusted to play in the Premier League before October 20, then only deemed able to play as one of two holding midfielders. Now he is the lone defensive midfielder, a forceful, physical specialist, rather than the converted No 8s such as Henderson, Gini Wijnaldum and Emre Can that Klopp, in examples of leftfield thinking, had used. The strength of that spine has been pivotal. Liverpool have had a pragmatic rebrand, no longer as blisteringly eviscerating as they were, but more consistent. Lacking Manchester City’s capacity to turn contests into exhibitions, their games are tighter, tenser, tougher. Since February, Liverpool have only had the comfort of a two-goal lead for 64 minutes in the Premier League, compared to City's 167. They have trailed twice whereas City have not been behind at all. With narrow margins and great expectations, the situation has been one of perpetual pressure. That spine has not buckled. Whether or Liverpool transport us back to 1990, they have shown a formidable backbone.