These two clubs are the clearest examples of the impact foreign investment can have - and has had - in England, with both teams possessing histories highlighted with modest success and sporadic trophy triumphs until takeovers by wealthy foreign owners propelled them to the top of the game.
Roman Abramovich led the way for Chelsea in 2003; the Blues had won just one league title before that, but they have since lifted both the Premier League and the FA Cup five times apiece, in addition to two Champions League crowns - most recently at Man City's expense - and another two Europa League triumphs.
Man City's transformation into a footballing superpower is even more recent, winning seven of their nine domestic top-flight titles within the past 12 years and making history by winning the treble of Premier League, FA Cup and Champions League last term.
Double-treble dreams were dashed by Real Madrid in midweek as their Champions League defence came to an end, but they could still cling on to two of the trophies they won last season, with a win this weekend leaving them 90 minutes away from retaining the FA Cup for the first time.
While Chelsea have fallen on harder times in the last couple of seasons, these two have provided some of the greatest players to have graced the English game over the past two decades especially, although there are plenty of honourable mentions from their pre-takeover histories too.
Naturally for a pair of teams whose most successful periods by far have come this century, the below combined XI is made up of modern players who have helped to bring them that success, although all the standout names from the more distant past were considered for places.
Here, Sports Mole selects the all-time greatest combined XI from the histories of Man City and Chelsea.
Goalkeeper: Petr Cech
While Abramovich took over at Stamford Bridge in 2003, it wasn't until a year later, with the arrival of Jose Mourinho and the influx of influential players that followed, that their true reign of success began.
Petr Cech is right up there towards the top of the list when it comes to Chelsea's most influential buys, immediately establishing himself as a towering presence between the sticks. A clean sheet on his Premier League debut against Manchester United set the tone for what was to come.
In his very first season at Chelsea, Cech broke the Premier League record for longest time without conceding at 1,025 minutes - stretching almost three months - and the Blues shipped an astonishingly-low 15 goals all term - a Premier League record which still stands today.
Needless to say, Chelsea also won the title that season, one of 15 trophies Cech lifted with the Blues. That haul includes three more league titles, the Champions League, the Europa League, four FA Cups, three League Cups and two Community Shields.
Including a spell with Arsenal at the end of his career, Cech kept an unparalleled 202 clean sheets in the Premier League, and in total kept 228 clean sheets in his 494 appearances for Chelsea across all competitions.
Honourable mentions: Bert Trautmann, Peter Bonetti, Ederson, Frank Swift, Joe Hart, Joe Corrigan
Right-back: Kyle Walker
A previous iteration of this team had Cesar Azpilicueta at right-back, but Kyle Walker has since surpassed the former Chelsea stalwart and established himself as one of the best full-backs the Premier League has ever seen.
Even at 33 years old, Walker remains the benchmark for defensive pace in the English game, with his speed and reading of the play combining to make him an integral part of the Pep Guardiola side that has dominated domestically for a number of years now.
The England international is closing in on 300 appearances for the Citizens across all competitions, and in that time he has won all of the biggest prizes: five Premier League titles, two FA Cups, four League Cups, a Champions League, a FIFA Club World Cup and a UEFA Super Cup included.
Guardiola's relentless demands have seen Walker temporarily drop out of the first-choice XI at times, but he has always been able to adapt and reinvent himself, and will go down as one of the key figures of Man City's golden era.
Honourable mentions: Cesar Azpilicueta, Branislav Ivanovic, Pablo Zabaleta
Centre-back: John Terry, Vincent Kompany
Two titans, and two of the greatest captains club football has ever produced in this country - certainly in the modern era.
Both players were at the club before the mega-money arrived, yet still managed to prove themselves as the heart, spine and muscle of the team as higher-profile superstars were brought in around them.
John Terry was a Chelsea servant for 22 years, arriving in 1995 before coming through the ranks and making his first-team debut in 1998.
Nineteen years, 717 appearances and incredibly 67 goals later, the defensive stalwart said an emotional farewell to his boyhood club, moving on as their most successful ever captain, and the most successful captain in Premier League history.
Terry lifted the league title five times as skipper, in addition to five FA Cups, three League Cups, two Community Shields, the Champions League and the Europa League.
A two-time Chelsea Player of the Year and three-time UEFA Defender of the Year, Terry can lay a strong claim to being Chelsea's greatest ever servant.
Kompany's arrival at Man City came just before the mega-investment, and he proved to be one of the best bargains of the Premier League era as he inspired the club to trophy after trophy.
Like Terry, Kompany developed an uncanny knack for not just keeping goals out, but also scoring big ones at the other end - most notably one in the Manchester derby en route to the 2011-12 title, and his long-range screamer against Leicester City en route to the 2018-19 crown - both crucial moments in two of the tightest title races in recent times.
In all, Kompany scored 20 goals in 360 appearances for Man City, but both tallies would have undoubtedly been higher had he not been so blighted by injuries throughout his career.
Even so, it speaks volumes that a player who only managed to play more than 28 league games in three of his 11 seasons at the club is so highly regarded.
The Belgian left in 2019 with a fourth Premier League title to his name, in addition to winning two FA Cups, three League Cups and two Community Shields, and being named the Premier League Player of the Season in 2011-12.
Honourable mentions: Ron Harris, Ruben Dias, John Stones, Ricardo Carvalho, Marcel Desailly, Mike Doyle
Left-backs: Ashley Cole
Ashley Cole's switch from Arsenal to Chelsea in 2006 earned him widespread condemnation, not just from Arsenal fans but others who felt it was a money-chasing move from a boyhood club to a direct London rival.
Looking back, though, few would argue against it being a good decision. Already England's standout left-back, Cole took his game to a new level at Stamford Bridge and achieved the ultimate goal of Champions League glory in 2011-12.
Cole did only get his hands on the Premier League trophy once at Chelsea, but he made up for that with four FA Cup crowns to make him the most decorated player in the history of the oldest football competition in the world.
Add to that a League Cup, Community Shield and Europa League and Cole boasts an enviable trophy cabinet from his Chelsea days, before eventually leaving on a free transfer in 2014.
The England stalwart ended his time at Stamford Bridge having made 338 appearances - 110 more than he did for Arsenal - and with seven goals to his name.
Honourable mentions: Graeme Le Saux, Glyn Pardoe, Paul Power
Central midfield: Kevin De Bruyne, Frank Lampard
It may not be the most defensively-minded central midfield pairing available - and the likes of N'Golo Kante, Claude Makelele, Rodri or even Yaya Toure would be worthy inclusions in a more balanced team - but really, how could we leave either Kevin De Bruyne or Frank Lampard out?
De Bruyne only narrowly missed out in our first iteration of this team in 2021, but he has continued to go from strength to strength and has now established himself as one of the first names on this teamsheet.
A former Chelsea player himself, De Bruyne has been the talisman of Guardiola's Man City for almost a decade now, providing crucial goals and, more notably, assists galore throughout that time.
The Belgian is closing in on 400 appearances for the Citizens - despite suffering a couple of injury-affected seasons during his time at the Etihad - and has scored over 100 goals in that time, while registering more than 160 assists.
De Bruyne's trophy cabinet reflects that too; he boasts five Premier League titles, two FA Cups, five League Cups, a Champions League and a FIFA Club World Cup to his name on a team level, while individually he is a four-time Man City player of the year, two-time Premier League and PFA Players' player of the year, three-time Premier League playmaker of the season and five-time member of the Premier League Team of the Year.
Joining De Bruyne in the heart of this team is a former teammate of his at Stamford Bridge - Chelsea's record goalscorer Frank Lampard, who can lay a very strong claim to being the single greatest player in his club's history.
Lampard was tipped for a bright future when he arrived from London rivals West Ham United for £11m in 2001, but no one could have expected him to go on and enjoy such a level of success at Stamford Bridge.
By the time he left 13 years later, Lampard had become the club's best-ever goalscorer from midfield as legendary strikers were left in the wake of his remarkable scoring record.
The England man netted 211 times in his 648 Chelsea appearances, including five consecutive seasons of 20+ goals from 2005-06 to 2009-10 - peaking at 27 goals in the latter year.
Alongside John Terry, Lampard was the bedrock of Chelsea's success during that time, not just surviving the major overhaul after Abramovich's arrival, but thriving and emerging as the first name on the teamsheet.