This week marks the 10-year anniversary of one of the biggest results in Pompey's post-war history.
And one no-one - even the most optimistic of Blues fans - can really admit to have predicted.
Back on March 8, 2008, Harry Redknapp's side headed to Manchester United for an FA Cup quarter-final tie.
At the time, Pompey were going strong in the Premier League, with Harry Redknapp's side sitting ninth in the table and on course for their highest-ever Premier League finish.
But in Alex Ferguson's Red Devils, they faced an outfit who were reigning Premier League champions - and a team in hot pursuit of the treble.
The odds were heavily stacked against them - a fact reinforced by the Blues' 2-0 defeat at the hands of United at Old Trafford back on January 30, just five weeks previous.
So on that basis alone, the Blues had no right to silence the growing sense of invincibility that had been gathering among Ferguson's high-flying squad of seasoned internationals.
Yet, they did, with Sulley Muntari's 78th-minute penalty proving the difference on a dramatic day.
The victory, of course, put Pompey in the driving seat to go on and claim FA Cup glory.
It was an invitation they gratefully accepted, with Kanu's goal against Cardiff in the final at Wembley the crowning moment.
But should Pompey really have got that far in the first place?
Their visit to Old Trafford should surely have been the end of the road for them - and there would have been no harm in that.
Indeed, comparing the two starting XI's that Saturday afternoon, a vast gulf separated the two sides really.
The team that Ferguson put out that day included four Champions League winners - Edwin van der Sar, Wes Brown, Owen Hargreaves and Paul Scholes.
Van der Sar, Brown and Scholes had alsoPremier League winners' medals in the bag, as had Rio Ferdinand, Patrice Evra, Nemanja Vidic, Cristiano Ronaldo and Wayne Rooney.
Meanwhile, Hargreaves had multiple Bundesliga medals with Bayern Munich.
Only Nani and Carlos Tevez had failed to deliver some of the biggest prizes in world football.
Yes, the visiting Blues had a Champions League winner and Premier League champions in their line-up.
Kanu won Europe's most prized possession with Ajax in 1995, and had two English titles on his CV from his spell at Arsenal - plus two FA Cups.
Glen Johnson and Sol Campbell (two) had also lifted the Premier League title with Chelsea and Arsenal respectively, with Campbell also being involved in three Cup victories.
Yet the rest of the team that day had nothing really to shout about in term of the major honours.
David James had won a League Cup with Liverpool, while Lassana Diarra was an unused sub in Chelsea's Cup victory over United in 2007.
Sylvain Distin, Hermann Hreidarsson, Niko Kranjcar, Papa Bouba Diop, Sulley Muntari and John Utaka had yet to make their mark in English football.
The cost of assembling the two teams that day is also contrasting.
The United side that walked out at Old Trafford back then was put together at a cost of around £122million.
Scholes and Brown were graduates from the Red Devils' youth set-up.
The rest were purchased for big money.
Ferdinand was signed from Leeds for £30m, Rooney came from Everton with a £25.6m price tag attached, Nani arrived from Sporting Lisbon for £22.5m, Hargreaves was a £17m addition from Bayern, while Ronaldo was a £12.24m signing from Lisbon.
Tevez was on loan from West Ham at the time, but would cost United £35m in July of that year.
Despite not wanting to been termed a wheeler dealer, Redknapp's side cost £31.8m.
Muntari and Utaka were the biggest outlays at around £7m each, from Udinese and Rennes respectively.
James arrived for £1.2m from Aston Villa, Johnson was a £4m buy from Chelsea, Diarra cost £5.5m from Arsenal, while Kranjcar and Diop were £3.5m each from Hajduk Split and Fulham.
Four of the team that day were actually free transfers.
Campbell (Arsenal), Distin (Manchester City), Hreidarsson (Charlton) and Kanu (West Brom) were all out of contract and arrived without a fee having to be paid.
Of the back four that day, only Johnson had required a exchange of money.
In total, the silverware accumulated by the two teams before and after that last-eight clash also differs staggeringly.
At the time United's galaxy of Champions League winners, Premier League champions etc had celebrated 84 trophy successes, as opposed to Pompey's 38.
For those involved that day, those figures now stand at 208 and 64 winners' medals respectively.
Proving that that United side were not only perennial winners at the time but players with the potential to go on and dominate their sport for even more years to come.
Upon his retirement from the game in 2013, Scholes had amassed 25 trophies and is now the most decorated English player of all time.
Ronaldo currently has 25 major titles to his name, as well as a then world-record transfer fee following his £80m move from United to Real Madrid in 2009.
Meanwhile, van der Sar finished his career with 27 honours.
Kanu remains the Blues' most decorated player from the game, with Champions League, UEFA Cup, Premier League (2) and FA Cup (2) winners' medals to look back on fondly.
Muntari and Diarra are the only two who built on their Cup success with Pompey, with league titles in Italy and Spain respectfully.
United's class of international stars did, of course, go on to claim Champions League victory and the Premier League title back in 2008, with their defeat at the hands of the Blues only one of two in all competitions since the middle of February of that year.
Pompey finished a record-high eighth, with their success that season providing them with their first ever taste of European football.
We all know the club's troubles since then - and how mega-rich United continue to be a driving force in today's game.
But 10 years on from that day, memories remain fresh of the day the Blues defied the odds on one of the world's biggest stages and stopped a footballing power house in its tracks.