Serial winner v serial entertainer: Klopp has yet to match Mourinho's ability when it comes to winning silverware
When these sides met six months ago, there was a real sense that a rivalry seeped in historic animosity might provide us with some evidence that one of the pair could be primed for a title challenge.
Free-scoring United had gone into that game with 10 wins and a draw and were level with their city neighbours but approached the contest with a visible lack of intent, notably deploying the rarely-used Matteo Darmian at left-back with Ashley Young on the right in front of Antonio Valencia.
It seemed odd, even at Anfield, because Liverpool had won just one of their previous seven games in all competitions and, at that stage, were three points behind Watford, mired in mid-table.
Six months on, Manchester City's remarkable odyssey has over-shadowed them both and, although European prospects remain - and another tilt at the FA Cup for United - they are now merely vying for the runners-up spot.
David De Gea's left-footed reflex save - he has become overly familiar in producing such world-class stops - from Joel Matip was the highlight of a dour scoreless draw when Jose Mourinho deflected criticism of his own side's tactics by baiting Liverpool about theirs.
Since Mourinho arrived at Old Trafford as manager in 2016 as Louis van Gaal's successor, this fixture has lacked the fizz of yore.
Three games finished as draws, with just two goals in 270 minutes of football and United registering five shots on target.
And yet, despite the fact that many feel Liverpool are best-placed to launch a counter-offensive next season, United remain ahead of them in the league and Mourinho, the serial winner, has already banked two major trophies during his time at Old Trafford.
Jurgen Klopp team's have won nothing yet.
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For both of them, the reality is that being 16 points behind the first-placed side is no huge boast. Second is nowhere; the only time it is relevant at all is when you should have finished first, like Arsenal or Spurs in their futile challenge to Leicester two seasons ago.
Mourinho's aims cannot again be limited to an honourable draw today, especially at home and, quite aside from their neighbours' looming shadow, it will rile him that there has been a lot more praise and excitement about Klopp's improvement of Liverpool compared to that effected by himself at United.
His methods, although disparaged by some, have proved themselves for a much more sustained period of time than Klopp's, who has yet to translate a winning style into tangible success, apart from his brief winning spurt with Dortmund.
He has lost two winnable finals with Liverpool. Mourinho has already won two finals with United; his focus is success at all costs.
The German has had to ignore criticism of this style, just as Mourinho has suffered his own barbs down the years for the way his teams play and his occasionally cavalier treatment of players.
Mourinho's method owes much to the modern way in that he builds impressive winning teams with little regard for the individual development of players.
This is Klopp's greatest strength, even if he has yet to match the Portuguese maestro's ability to carve successful teams.
We will see one of them today.
Mohamed Salah has been a revelation for Liverpool this season but this is a player who was once off-loaded by Mourinho who, unlike Klopp it seems, didn't have the patience or empathy to produce the best of his ability. Few of us recognised the possibilities but Klopp did.
The most vivid image of the manager this season is how he warmly hugs and cajoles each of his team; Mourinho lacks that quality as a former Klopp favourite, Henrikh Mkhitaryan, discovered to his cost.
The Armenian was moulded by Klopp at Dortmund into an attacking, goal-scoring midfielder - 23 goals in 52 games in one season - and there was considerable celebration within Old Trafford, vocally expressed by Mourinho, when his signature was captured.
However, he soon became a fall guy and never really recovered from being withdrawn at half-time against Manchester City.
He became a bit-part player and couldn't respond to Mourinho's tough love.
The United boss moved him on but he is still scratching for his preferred line-up; he remains an expert at selecting teams for particular matches but, in contrast to Liverpool's defined style of play, and relatively unchanged line-up, United's inconsistency and the fitful form of key players demonstrates that fact.
For example, marquee signings Paul Pogba and Alexis Sanchez both arrived from teams which had a recognised style of play but they are now at a team where that hasn't happened and they are both struggling.
Teams should have effective combinations. A central defence and goalkeeper are the basis of a successful team. If that isn't right, you're in trouble.
There is the relationship between the full-backs and the players on either flanks; then the midfield pairing and, depending on the formation, the front man and whoever is beside or just behind him.
At United, there is not that sense of intuition within the team. Nemanja Matic cannot rely on Pogba to track back; neither full-back has as yet developed a reliable understanding with Sanchez or Anthony Martial. Or whoever is playing on the flank this week.
Up front, Romelu Lukaku can get isolated from all his partners as we saw at Anflield and also the recent game in Sevilla.
There is not a clear enough spine to their side either for all their physicality. Both his title-winning teams with Chelsea had all these attributes.
Klopp is more acutely aware of his needs. Virgil Van Dijk was a much-needed capture and has provided a clear impact. (So would a goalkeeper, by the way).
For United, Pogba and Sanchez were available but their arrival has neither led to a more settled environment nor a clearer style of play. Sanchez in particular looks very similar to the frustrated figure before he left Arsenal.
Despite losing Philippe Coutinho, Klopp's team has continued seamlessly.
Who will be the centre-backs for United today? Eric Bailly was the preferred option earlier in the season until injury but the less experienced and error-prone Victor Lindelof has remained ahead of him lately.
Since signing Van Dijk from Southampton, Klopp's defence is much more settled.
Liverpool's team selection seems relatively straightforward - Karius, Alexander-Arnold, Van Dijk, Lovren, Robertson; Henderson, Can, Oxlade-Chamberlain; Salah, Firminio and Mane.
It is a much tighter squad with perhaps James Milner and Georginio Wijnaldum as midfield alternatives.
Klopp does rotate but he is much more reliant on form and with his focus narrowed to two competitions, changes should be minimal.
It's much more difficult to second-guess Mourinho.
De Gea, Smalling, Valencia, Matic and Lukaku are perhaps nailed on - Pogba and Sanchez are arguably there by reputation alone rather than current form. Everyone else is interchangeable.
Martial may be on the right but that combination hasn't worked. Jesse Lingard and Marcus Rashford have made impacts from the bench but, as we mentioned after the arrival of Sanchez, one of these younger players must lose out.
He has plenty of options but has yet to alight on the correct combination. Against Palace in the last quarter, all sense of caution was abandoned as United rescued an apparent lost cause, with six attacking players.
It may have been a thrilling finale but finding the consistent rhythm remains elusive.
In contrast, you sense that Klopp is more content with what he has at his disposal.
As it stands now, aside from De Gea, it is difficult to work out which United players a Liverpool supporter would covet for their team
I'm sure that Klopp would fancy trying to improve Pogba though, particularly in the light of the transformative effect he has had on the career of Wijnaldum, an average performer in Newcastle's relegation struggle, but one who Klopp has featured in the front three at times as well as his usual midfield role.
United would like to have better full-backs and while neither side would swap what they already have, Liverpool's improving pair are better in my opinion. Their central defence is stronger now with the presence of Van Dijk.
In midfield, Matic is probably superior to Henderson but it is difficult to argue that Herrera or McTominay trump Can or Oxlade-Chamberlain on current form. Mourinho might like Can if he could get him.
Up front Mourinho has always liked a strong front-man - Didier Drogba, Diego Milito, even Emmanuel Adebayor during a loan spell - whereas Klopp discarded Christian Benteke.
The German likes players with elaborate movement and pace whereas Mourinho has moved Martial and Rashford to the wider positions.
Klopp might have taken Sanchez had he the budget when Coutinho departed; he would have fitted in more naturally under his tutelage you feel.
There is no argument about whose front three are superior. Their presence should define today's encounter in terms of how much damage they can cause and, against that, how effective Mourinho can be at limiting their impact.
Liverpool have scored 34 league goals away from home - a joint-high in the top five European leagues (level with Lyon) - with 10 in their last three away games and much of the early-season fears about their defence has now dissipated.
Mourinho has won only one of his eight meetings in all competitions against Klopp sides, yet of his 50 league games at Old Trafford, he has lost but two - both to City.
For all that, United must produce something more incisive in attack to thwart Liverpool's fearsome front men.
With Liverpool having much the easier run-in, another drab draw will not do for United, who return here during the week knowing they will also need to score to stay in Europe.
The fact that his side already have more wins (19) and goals (56) than at this stage of last season demonstrates they have the ability.
The debate may rage on about United's progress and style but for their manager, and supporters, today's argument is all that matters for now.
- Manchester United v Liverpool, Live Main Event, Sky Sports, 12.30