Manchester City have always regarded Liverpool as the team to watch in the rear-view mirror during all their years of unprecedented success under the regime of Pep Guardiola.
Jurgen Klopp's powerhouse Liverpool side have pursued them every inch of the way in Premier League title races, even unseating them in one for their first crown in 30 years, while inflicting painful defeats in the Champions League and FA Cup.
In other words, the one domestic team that would always worry Guardiola, who once in admiration described them as a pain in a sensitive part of his anatomy, was the Liverpool Klopp built.
Liverpool, in this mediocre and mostly joyless season, were still able to rouse themselves to beat City 1-0 in a thunderous Anfield encounter last October.
Not in a thoroughly chastening 90 minutes at Etihad Stadium for Klopp and his Liverpool players as City won 4-1 and could have won by more; the gap that has been opening up between the two pre-eminent powers of recent years suddenly resembling a chasm.Man City thump LiverpoolFollow all the Premier League action
Liverpool, who will end the season without silverware and are now struggling for a place in the Premier League top four, may just have scented a chance when the City team-sheet landed without striker Erling Haaland, the 42-goal colossus, and with Phil Foden also out after appendix surgery.
And Liverpool will have felt even better when they caught City with a sucker punch on the break and Mohamed Salah put them ahead after 17 minutes.
It was all downhill for Liverpool from there as City produced a magnificent team display to run out easy winners.
Guardiola, even with this convincing win to celebrate, described Liverpool as "the biggest rival I have had in my career. The team where we have always struggled to find a way".
It is a sign of just how far two teams who have spent so long as each other's shadows have drifted apart that City did not struggle to find a way here, even stripped of Haaland. They found ways constantly and Guardiola's only gripe was that they could have inflicted humiliation on their old rivals had they taken all their opportunities.
City have hit a hot streak of seven straight wins and a sign of their strength is that Argentina's World Cup winner Julian Alvarez stepped seamlessly into the shoes of Haaland, scoring one goal and making another.
Guardiola's tactical switches often raise the eyebrows but his ploy here of pushing John Stones into a slightly more advanced midfield role worked a treat as he showed the poise and wisdom of a natural, spraying passes around with perfect weight and breaking up attacks while still showing aerial dominance in his own area.
At the heart of it all, however, was Jack Grealish.
Grealish took time to settle at City but has shown his quality this season and nothing has been better than his performance here.
He made Alvarez's equaliser and scored City's fourth before leaving to a standing ovation but his whole performance was summed up by a selfless contribution that may just have changed the face of the game.
Liverpool were leading 1-0 when Salah broke clear with the option of either going alone or playing in Diogo Jota with only City keeper Ederson to beat. Etihad Stadium held its breath then rose in a giant roar as Grealish raced back to thwart Salah.
Seconds later Grealish was setting up Alvarez's leveller and City were on their way.
Liverpool's players looked downbeat as they made their way off. By then, many of their supporters were already back on the M62 heading west.
Klopp looked and sounded dejected in his post-match address. He said he will recover but can the same be said of a Liverpool team clearly in decline, one that has suffered dreadful defeats by Bournemouth and Manchester City, with a Champions League exit to Real Madrid sandwiched in between, since they beat Manchester United 7-0?
And perhaps they are displaying classic symptoms of a once great team on a downward curve. They go into decline, have occasional flashbacks to what they used to do and stick seven past Manchester United, then go back to being in decline again.
Liverpool had a case that Rodri could have been shown a second yellow card in the first half, although referee Simon Hooper did not require six players in red shirts swarming him offering advice on that he should do.
Much has been made of Liverpool's interest in Borussia Dortmund teenager Jude Bellingham, a deal they will pursue despite a price tag likely to be in excess of £100m and with interest from rivals such as Manchester City and Real Madrid.
Make no mistake, he would be a brilliant addition if they could pull it off but it is a grand delusion to think Bellingham is the answer to all of Klopp's problems.
Fabinho and Jordan Henderson looked over-powered and out-run in midfield well before the final whistle. Virgil van Dijk is now vulnerable, the old invincibility long gone, while Trent Alexander-Arnold's flaws at right-back are not only well-chronicled but increasingly a concern for Liverpool.
There are failings that need to be addressed in several areas and Bellingham cannot cover them all. The sight of Salah being substituted with 20 minutes left did not just smack of saving him for Chelsea on Tuesday night, it smacked of surrender.
Klopp made five substitutions before Guardiola made one. This was a manager searching for solutions he currently cannot find.
Liverpool and Klopp's main priority is that top-four finish and they will need to recover some of their old authority quickly to achieve it - namely by Tuesday at Stamford Bridge.
At season's end, Klopp's team that has served him so thrillingly over the last few years is in need of re-assembly.
Manchester City's vast superiority, even without the striker who has dominated the season, will have hurt Klopp and Liverpool desperately.
It not only showed how far they have fallen behind, but what a vast task it will be to get back in sight in that mirror again.
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