This weekend's clash between Liverpool and Manchester City is unquestionably between the two best sides in the Premier League, if not European football, but it was a different matter entirely in November 2015.
Liverpool had finished sixth the season prior, and doubts remained over whether manager Jurgen Klopp would enjoy the same kind of success in England that he had had with Borussia Dortmund in Germany.
A 4-1 win at Etihad Stadium, however, emphasised the impressive progress being made by the Reds under Klopp – it was his first away win over City – but, from the hosts' perspective, the result confirmed that they were now going backwards under Manuel Pellegrini, after winning the title just two years before.
Indeed, a little over two months later, the Chilean was shown the exit door at the Etihad, and he would be replaced by Pep Guardiola, thus paving the way for the clash of the titans we will witness on Sunday.
Few in the Man City team that faced Liverpool seven years ago lasted long under the new boss.
Joe Hart, Bacary Sagna and Jesus Navas were among those jettisoned, but nobody suffered a bigger fall from grace than Eliaquim Mangala.
The centre-back's own goal in that loss to Liverpool still makes for painful viewing today.
Roberto Firmino's cutback to the edge of the six-yard area is met by Mangala doing his best baby giraffe impression, his tangled legs inadvertently directing the ball into the bottom corner in painfully slow and comical fashion, past the despairingly wrong-footed Hart.
For Mangala, it was his Etihad career in a nutshell, a condensing of a stint where he often looked confused, immobile and a long way from the player Man City had signed from Porto for £42 million ($55m) in 2014.
Mangala had been tipped for the top of the game ever since being converted from a striker to a defender at Standard Liege, whom he had joined aged 17.
He worked his way up to the first team before being signed by Porto in 2011, where he attracted the attention of leading clubs around Europe after winning consecutive Primeira Liga titles.
A long-term target for Man City – who attempted to sign him in January 2014 but aborted their efforts when Porto demanded more than £50m ($65m) – he eventually found his way to the Premier League that summer as the second-most expensive defensive transfer in British football history.
There were perhaps ominous signs of things to come in the difficulties surrounding Mangala.
The months of delay in City confirming the move saw Chelsea attempt to scoop them at the last minute, while a video of his welcome interview was posted on the City website before the deal was officially announced. The club claimed they were hacked.
His Premier League debut was also delayed until the fifth game of the season in late-September, but looked to contain great signs of things to come, as he impressed alongside Vincent Kompany in a 1-1 draw with Chelsea
However, in his very next outing, a 4-2 win over Hull, he scored an own goal and conceded a penalty.
Goal/GettyPellegrini refused to blame Mangala after the game, while Kompany was also quick to jump to his new team-mate’s defence.
"The rest of the game, he played well, he stayed professional,” he told reporters. “You could not have asked for more.
"The main thing is to stick to your job, sometimes you get a half an hour like this. I've seen in him a great reaction and in the second half he was spot on."
In fact, Mangala's stats at Man City were not dreadful – 41 wins from 59 Premier League games, only nine defeats, a 78 per cent successful tackle rate and 22 clean sheets.
However, it was the nature of some of those defeats which defined his time in England, with that meeting with Liverpool in Manchester the standout fixture.
Guardiola's arrival also effectively signalled the end of Mangala's time in the first team, as he was sent out on loan to Valencia for the 2016-17 campaign.
After a brief spell back with City for the first half of 2017-18 – when he played nine Premier League games, enough to earn him a winner's medal as City romped to the title with 100 points – a loan stint at Everton ended after two games due to injury.
"Manga helped us this season. I don’t have doubts about the specific qualities Manga has," said Guardiola in January 2018. "Defensively, he is a top, top, top player."
Yet by the time he eventually left Man City in summer 2019, Mangala had not played a competitive game in more than a year, little more than a ghost haunting the Citizens after being totally disregarded by Guardiola.
A permanent move to Valencia in 2019 was interrupted by the coronavirus pandemic in early 2020, and he is now on a temporary deal at Saint-Etienne battling relegation from Ligue 1.
It would be no surprise to see him moving on again when the contract expires in the summer.
Nowadays, Mangala is only remembered in Man City circles as a byword for a dodgy defender, such as when Micah Richards used him as an unfavourable point of comparison for a poor performance by Kalidou Koulibaly in August 2020, who was then heavily linked to the Citizens.
Richards told CBS Sports: “Everyone talks about how he [Koulibaly] is supposed to be composed on the ball, he's aggressive, but I see similarities to Mangala – and he went to City and it didn't really work out for him there, so I'm not totally convinced after that performance.”
Ultimately, Mangala flattered to deceive on the pitch, obvious signs of quality – such as a fantastic back-heeled volley scored in training in April 2016 – too often counter-balanced by poor decision-making and a lack of composure on the ball.
Whatever happens on Sunday when the top two teams in England clash at Etihad Stadium, it should be a reminder of just how far both teams have come since 2015.