Momentum. Manchester United have found it; Liverpool have lost theirs.
But if there is any certainty about this weekend’s Old Trafford encounter between English football’s most successful and celebrated clubs, it is that the “M” word can be transferred from one to the other within 90 minutes on Sunday.
United, five points adrift of second-placed Liverpool in sixth place, are aiming to record a 10th successive victory in all competitions this weekend, with Jose Mourinho’s players now on the club’s best run of form since 2009.
Liverpool? Wednesday’s 1-0 defeat against Southampton in the EFL Cup semifinal first leg at St Mary’s was only their third reverse of the campaign — all of which have come while wearing their awful ‘Toxic Thunder’ green away kit — but it was also their third successive game without a victory and second consecutive game without a goal.
Less than two weeks ago, Jurgen Klopp’s team dispatched Manchester City at Anfield in a 1-0 victory on New Year’s Eve, which appeared to cement their status as the biggest threat to leaders Chelsea in the race for the title. But as they head to Old Trafford, the feel-good factor of that win has evaporated, and it is Liverpool who approach the game with anxiety and trepidation.
They have hit their first wobble of the season, and it could not have happened at a worse time.
But while the form guide favours a United team who also have the advantage of a fully fit squad, with the likes of Michael Carrick and Zlatan Ibrahimovic rested in the lead-up to the game, the significance of the fixture is the same for both clubs.
Mathematically, it is a game that Liverpool can afford to lose in the sense that they would remain two points clear of their historical rivals, whereas a United defeat would end their flickering hopes of an unlikely surge to the title and also potentially push them six points off the pace in the race for Champions League qualification.
But psychologically, there is arguably more at stake for Liverpool than United.
If United lose, it will certainly hurt Mourinho and his players, but they are playing catch-up and remain outsiders in the battle for the top four.
Defeat would be a setback for United, but it would not have the same corrosive effect on morale and confidence that it could have on Liverpool if Klopp’s team allow United to make it 10 wins in a row and move to within two points of them.
United’s momentum would then be given a turbocharge, leaving Liverpool looking anxiously over their shoulder with a creeping feeling of self-doubt beginning.
Two weeks after signalling themselves as Chelsea’s closest challengers, Liverpool could instead find themselves contemplating the nightmare scenario of dropping out of the top four.
United are simply fighting to catch up, but Liverpool are aiming to safeguard their position and prove their credentials, so there is a subtle difference in the mindset of both teams as they go into the game.
A draw suits neither team, such is the ferocity of the battle for position within the top six, but a defeat would as good as end the loser’s hopes of achieving their primary ambition — Liverpool winning the title and United climbing into the top four.
But it all goes back to momentum, because it has become a quirk of English football that its two biggest clubs have been unable to enjoy the sensation of moving forward at the same time in recent seasons.
When one has been up, the other has been down, and vice-versa.
United and Liverpool have not been direct rivals in a title race since the 2008-09 season — the campaign which saw Rafa Benitez attempt, and fail, to gain a psychological victory over Sir Alex Ferguson by producing his infamous list of “facts.”
And not since that season, when United finished champions ahead of Liverpool, have the two clubs finished together in the top four and qualified alongside each other for the Champions League.
When Liverpool ended their five-year exile from the Champions League in 2014, United failed even to qualify for Europe having finished seventh under David Moyes the previous season.
So Sunday may ultimately be about which team claims the momentum for the second half of this season — the momentum which could propel them towards achieving their target and send their biggest rivals into reverse.
Form and fitness are in United’s favour, with only Eric Bailly unavailable to Mourinho due to the Ivory Coast defender being away on international duty at the Africa Cup of Nations.
Klopp, meanwhile, is without Sadio Mane for the same reason, but the Liverpool manager must also find a way to restore captain Jordan Henderson and defender Joel Matip to the team, despite doubts over their full fitness following recent injury layoffs.
Philippe Coutinho’s return from injury as a substitute at Southampton is a positive for Klopp, but it was the Brazilian’s first appearance since late November.
Is Coutinho fit enough to make a difference at Old Trafford, and can Henderson and Matip last for 90 minutes against United?
Klopp has more questions to answer than Mourinho does, and, despite being above United in the table, the same applies to his team.
Sunday will answer many of those questions and tell us which of these superpowers will be the team to watch between now and May.
Mark Ogden is a senior football writer for ESPN FC. Follow him @MarkOgden_