Jurgen Klopp and the FA Cup will never be the closest of bedfellows.

He is not likely to mourn the fact that Liverpool 's wait to win the world's oldest cup competition will stretch into its 16th year for too long.

Despite that, the Reds boss will still leave Old Trafford with pangs of frustration.

Considering the opponent and the venue, this was about as well as Liverpool have played in weeks, but they will have nothing to show for it when the team meeting is called on Monday morning.

A rotten 2021 goes on.

The one perverse bright spot was the fact that 9,000 travelling supporters were unable to attend to witness the latest tumble.

They will save their voices for brighter days in Manchester.

Any indication as to how seriously Klopp was taking this game was always going to be revealed by his team news, but his Friday revelation that Mohamed Salah would be starting offered enough clues as to its importance.

The game's magnitude was probably down to its potential to reinvigorate more than any burning desire to see the fifth round, but the identity of the hosts will have no doubt played a part in the German's pre-match thinking.

Liverpool can simply never phone it in when they play Manchester United, regardless of any manager's favourable credit score with supporters.

In fairness, they didn't. But a streetwise United were able to take full advantage of a visiting side wrestling with a confidence crisis right now.

Klopp made five changes for this one as Joel Matip was wrapped in cotton wool and told to stay on his couch ahead of Thursday's return to Premier League action at Tottenham.

Manchester United vs Liverpool FA Cup

Captain Jordan Henderson also missed out as Curtis Jones was given a role on the left of a front three in place of Sadio Mane. Salah and Roberto Firmino were recalled after sitting on the bench for an hour of Thursday night's shock defeat against Burnley.

The decision paid off as they showed that their class is permanent for the opening goal.

Firmino split the United defence with a lovely through ball and Salah did the rest. The Egyptian waited and waited before dinking Dean Henderson with a sublime finish off his weaker right inside 20 minutes.

It all looked so easy, which makes it all the more baffling why a shot-shy Liverpool haven't netted in the Premier League since Mane scored against West Brom on December 27.

The lead was short-lived though as United found a way back through a counter-attack approach that reaped rewards all afternoon.

Marcus Rashford's raking pass put Mason Greenwood clean through and he dispatched past Alisson Becker.

The excellent Rashford caused an array of problems down Liverpool's right, particularly when Trent Alexander-Arnold was caught up field attempting to join the attacks.

The England international wasted little time picking up where he left off in the second period, apparently beating an offside trap to slot past Alisson for 2-1.

Rashford preyed on the inexperience of Rhys Williams, a player who spent last season on loan at Kidderminster, and it was quite simply a mis-match.

The calls have been growing for weeks and weeks but Liverpool's overwhelming need for another senior centre-back was never more apparent than here at Old Trafford.

Rashford made sure he made his quality and experience count against Williams as he gave the teenager a torrid afternoon.

The fact that Klopp has been expected to continue to keep Liverpool as the country's dominant side in the midst of this injury crisis, without the reinforcements he has readily admitted he would like, is borderline negligence from the owners.

Only they will know how tightly wound finances are right now, and given their prudent ownership over the last 10 years, they will no doubt see it as sensible leadership.

But while a stop-gap, mid-season centre-back continues to go begging, the Reds are losing significant ground.

Should the same problems rear their head at Spurs, it could be curtains for the defence of that Premier League title. It really is that grave a situation.

The relatively meagre financial rewards of the FA Cup are unlikely to force a shock re-think, but the game's biggest prizes - and their accompanying millions - could be out of sight within weeks at this rate.

Bleatings about transfer inactivity are surely futile at this stage, though. Klopp has made it crystal clear that he is not getting what he craves this January transfer window.

Even at their lowest ebb, however, Klopp's Liverpool have proven they have the stomach for the fight. Suddenly, it was 2-2 as they pounced on United's short goal kick to give Salah the chance to restore parity.

Another sucker punch awaited though as substitute Bruno Fernandes pinged home a free-kick on the edge of the box after Fabinho had felled Edinson Cavani.

Liverpool star Mohamed Salah

Get all the latest Liverpool injury and team news as Klopp faces selection dilemma, plus breaking news and analysis of what's next for the Reds.

You'll also get the latest transfer talk and analysis straight to your inbox every day with our FREE email newsletter.

Sign up here - it only takes a few seconds!

Xherdan Shaqiri and Divock Origi were summoned in place of an exhausted Thiago and Firmino but neither could do much to force an equaliser.

The sight of Williams getting caught in possession inside his own penalty area in the final seconds as Liverpool chased an equaliser just about summed it up.

The 19-year-old will no doubt have a very good career but circumstances have catapulted him to an area where he is out of his depth.

There is little shame in that from Williams' own personal perspective. He has had a season to remember as a Liverpool first-teamer, playing a big role in some important wins already this season.

He only made his debut at the end of September and this campaign will be an invaluable learning curve on his long-term journey.

But a club with ambitions as lofty as they are at Anfield should not be heading into the final week of the window in this shape.

The real concern is that it will take more than an FA Cup exit for those in power to realise it.