It's a rivalry that's been brewing since Jurgen Klopp and Pep Guardiola's days in the Bundesliga with Borussia Dortmund and Bayern Munich.
In total, the pair have faced off 14 times - with Klopp leading their head-to-head record by eight wins to five, with one draw. His record is even more impressive since they both headed to England - with Klopp only tasting defeat once in seven outings against Guardiola.
Despite that impressive résumé, Klopp has rarely threatened Guardiola's unparalleled record of success - watching on instead as the Spaniard secured back-to-back Bundesliga titles at a canter, as well as last season's Premier League title.
However now, their rivalry is seemingly taking on a whole new meaning, given the prolonged run of impressive form demonstrated by Klopp's Liverpool side. The Reds have often flattered to deceive, despite threatening to mount Premier League title challenges with periods of attacking brilliance. Defensively though, they have been calamitous - often falling by the wayside before the business end of the season has been reached.
This season though, those defensive worries appear to be behind them. Klopp unquestionably has transformed Liverpool from dreamers into genuine title contenders - a notion that Guardiola would have first sat up and taken notice of when the two teams met at Anfield last January.
At that point, City were already running away with the league, having gone on an unprecedented 18 match winning streak. Upon their arrival on Merseyside though, they would run into a Liverpool side hellbent on proving that the hype surrounding their front three of Sadio Mane, Roberto Firmino and Mohamed Salah had genuine substance to do it.
And substance is exactly what they would prove they had, as City - for the first time all season - demonstrated a defensive vulnerability that no other side had been able to expose. The Citizens were rattled, and within a nine minute period in the second half, had shipped three goals to trail 4-1. Mistakes had crept into City's game, and shellshocked by what was happening to them, they seemed all over the place.
Though they would run Liverpool close in the end with two late goals, they slid to a 4-3 defeat - their first Premier League loss and one to this day that sticks in the memory. For the Liverpool players and supporters, it proved to be a defining moment in their season. The raucous atmosphere generated on that night at Anfield proved to be the catalyst for an unexpected surge into the Champions League final - as well as qualification for this season's competition.
During that Champions League run, they would face up to City once more in the two legged quarter-final. Guardiola's side were overwhelming favourites despite January's result, having despatched the Reds in an early season encounter at the Etihad 5-0. Things had changed though. The mental scars were there for all to see, and in the first leg, Liverpool blitzed City once more to take a 3-0 lead after just half an hour.
The visitors would never recover, and despite putting up a grittier display in the second leg, they would fail to place Liverpool in the vice like grip that so many fall foul too at the Etihad. Klopp's side would win the game 2-1 to seal a 5-1 aggregate win. In doing so, the Reds put to bed the idea that they could be rolled over when put under pressure (by City that is) - demonstrating a previously unseen mental fortitude.
Now, the difference this season (or so it seems) is that Liverpool appear to have carried forward that momentum, and for once, they look unlikely to relinquish it - despite a Champions League defeat to Napoli in midweek and back-to-back winless outings against Chelsea.
Problem areas have been addressed with the signings of Virgil van Dijk and Alisson Becker, while Andrew Robertson and Trent Alexander-Arnold have transformed from promising full-backs into the full blown real deal. Couple those arrivals and sudden improvement in quality with the rejuvenation of James Milner and Georginio Wijnaldum in midfield, and Liverpool appear to have sharpened their tools for a proper push towards challenging City's dominance - much to Guardiola's dismay.
That drastic improvement, as well as their early season league results, prove that City will face an entirely different beast this weekend when they again travel to Anfield.
Only this time, there's more on the line than their last league encounter. This time, City could surrender their position of power in this season's title race. This time, Liverpool could grab all three points and send a real statement to Guardiola. This time, the tag of Premier League favourites could actually be up for grabs.
And although they wouldn't admit it, City's players will be feeling the pressure. Having cruised to the title last season (with seemingly consummate ease), the Citizens haven't experienced pressure in the league for 14 months - they were 15 points clear at the turn of last year after all. Now they'll be under the pump and bearing the scars of last season's results, as well as Guardiola's iffy record against Klopp. It'll be interesting to see how they react.
One thing is for sure. If Liverpool win, the landscape and feeling around this season's Premier League title race will be completely altered.