They and Man City play each other today and upset the applecart for a number of clubs
"I don't think he would have managed Newcastle forever. But I think he would have done for Newcastle what he did for another famous seaport team in stripes in Porto and he would've made his name and ended up in England whether it was with Chelsea or wherever."
That was veteran football journalist and Mourinho: Anatomy of a Winner author Paddy Barclay when Team 33's Richard Chambers once asked him a hypothetical question: What if Jose Mourinho had taken up Bobby Robson's offer to become assistant manager in 2000?
Football are full of such 'what ifs', many of which have yet to be uncovered.
Mourinho had worked as a translator for former Newcastle manager Robson when the late ex-England manager was coaching on the continent during the 1990s. Given where Newcastle are now, as a club which punch under their considerable weight, it's tantalising to wonder where the Magpies would be now if Mourinho had become Robson's successor at St James Park.
That's one question. But how about another? This weekend, Chelsea and Manchester City - who both undeniably owe all of their recent success to the money poured in by their respective owners Roman Abramovich and Sheikh Mansour - go head-to-head in the FA Cup fifth round.
It is also tantalising to wonder how clubs such as Newcastle and Tottenahm Tottenham were impacted by Chelsea's rise in particular as the summer of 2003 had a profound impact on the balance at the top end of the Premier League.
In the summer of 2003, Abramovich took over a Chelsea who were among England's Top 5 and had just secured Champions League football for the following season thanks to a Jesper Gronkjaer winner against Liverpool on the final day in what really amounted to a playoff for Europe's elite competition.
Newcastle had finished that season third ahead of both the Blues and Liverpool.
However, as Ken Bates handed over the keys to the future of Chelsea to the Russian billionaire, the Londoners had an estimated debt of £80 million secured against Stamford Bridge.
As The Guardian's Daniel Taylor wrote back in 2005, the threat of administration was a possibility.
Chelsea's John Terry (centre) celebrates his goal against Manchester City, with his team-mates Gianfranco Zola and Graeme Le Saux (right) during the Barclaycard Premiership match at Stamford Bridge, London. Picture by: Sean Dempsey / PA Archive/Press Association Images
The squad that summer had some ageing stars like Gianfranco Zola (35 at the time), Marcel Desailly (33) and Jimmy Floyd Hasselbaink (30), as well as a few future legends like John Terry (21) and Frank Lampard (24).
But Newcastle's squad was as strong as Chelsea's in 2002-03 - a season in which they had reached the Champions League second group stage and had their best league campaign since the heady days of the Kevin Keegan era as they finished third, 14 points behind champions Manchester United.
The squad itself had talent from goalkeeper Shay Given, Alan Shearer up front, Laurent Robert on the wing and other talented if injury-prone players like Kieron Dyer, Jermaine Jenas and Jonathan Woodgate. And the summer of 2003 saw them add the controversial but effective Lee Bowyer on a free.
Unfortunately 2003-04 also saw Newcastle slip back to 5th, as a Chelsea with a first wave of big money signings swapped places and rose to second under current Leicester City boss Claudio Ranieri. In their head-to-heads that season, Chelsea beat them 5-0 at Stamford Bridge, while the Magpies got revenge with a 2-1 victory at St James Park.
The Magpies haven't been back in the Top Four since and even endured relegation and other troubles in the meantime. Most of that can also be boiled down to bouts of incompetence and mismanagement of decisions, but if Chelsea had not benefited from a war chest which not only took the huge debt out of the picture but brought in a fresh wave of talent, would Newcastle have still maintained the gap above them by the following summer?
Chelsea managed to finish 23 points ahead of them in 2003-04 which was a swing of 25 points in one season thanks to a transfer surplus of over £100 million, including the arrivals of Damien Duff, Claude Makalele, Hernan Crespo, Adrian Mutu and Joe Cole.
With Arsenal, Manchester United and Liverpool still relatively strong in that era and Chelsea with seemingly bottomless trouser pockets, a new Top Four was established, locking out the teams below at a time when Champions League revenue began to create a gap between the haves and the have-fewers.
Over the last decade, Spurs have established themselves as a Top 6 club that can occasionally pierce the Top 4 fabric, despite often experiencing managerial instability. They certainly are on course to achieve at least a Champions League place this season under the astute Mauricio Pochettino as they find themselves above the wealthy Man City and Chelsea in the table, having beaten the former at the weekend.
There is a mini-connection between Abramovich and Tottenham, prior to the Russian billionaire's purchase of Chelsea.
In September 2003, Spurs chairman and ENIC Group co-owner Daniel Levy confirmed that he had met Mr Abramovich,"at his request because [Abramovich] wanted ENIC's perspective on the European football market. It is important to note however, that at no time did we discuss, either then or subsequently, his desire to acquire a Premiership club."
Tottenham Hotspur Chairman Daniel Levy (l) and manager Harry Redknapp watch from the stands in 2009 (Picture by: Mike Egerton / EMPICS Sport)
Abramovich bought Chelsea a couple of months after that meeting and years on, Levy probably wishes that the Russian had invested in another country.
Spurs first enjoyed some prominence towards the top end of the Premier League under Martin Jol in 2005-06 and 2006-07 at a time before Man City started spending heavily and during the years Chelsea were benefiting from both Abramovich's cash and Mourinho's expertise.
Arsenal finished above Tottenham on both occasions by margins of two points and eight points respectively and lest we forget that Everton were also just behind Spurs in the latter season.
But what if Chelsea had not had that cash flow? You could imagine that they would have slipped back into that upper mid-table battle which comprised the likes of Tottenham, Everton, Newcastle and sometimes Blackburn Rovers.
At least, you can imagine Tottenham could have once or twice finished the best of the rest behind Man United, Liverpool and Arsenal, even if self-inflicted instability did knock them back prior to Harry Redknapp's appointment as manager in 2008 when they arose again.
Arsenal's manager Arsene Wenger, center, looks on as Cesc Fabregas, right, and Robin van Persie, left, run during their open training session coinciding with the English Premier League soccer club's Members' Day at the Emirates Stadium in London, Thursday, Aug. 5, 2010. (AP Photo/Akira Suemori)
With the Emirates being built, Arsenal did face a trophy drought between 2005 and 2014, but the pain may have been less acute if Arsene Wenger's rebuilding of a new post-Invincibles team did not have an enriched Chelsea - and later Man City - to also battle with.
Manchester United, interestingly, did rebuild from a slightly lower ebb to eventually topple Chelsea in 2007, 2008 and 2009 in the era that English football enjoyed a level of dominance in Europe.
Partly, Chelsea's rise and consequent stabilisation of the Top Four may well have been one factor in a period which saw United win the Champions League in 2007-08 as the challenge posed by the Londoners brought the best out of Alex Ferguson's side in a way more significant than the Premier League battle.
And unfortunately for Liverpool, their descent out of the Top Four in Rafa Benitez's final season was not helped by the fact that Man City had come into some money and have since finished above the Reds in every Premier League season including the 2013-14 Luis Suarez-inspired title chase that fell just short.
Course, these are all 'what ifs'!