The Stretford Enders briefly stopped singing Ruben Amorim's chant professing their backing. It eventually restarted. The night ended to the sound of 'Friday I'm In Love' from The Cure.

Sir Alex Ferguson was yawning at one point. Come added time, he was fighting off fans attempting to embrace him in the directors' box. Another win in his time. Fergie Time.

United were unwatchable and unbelievable. Their first half performance was so atrocious the first team coach Darren Fletcher left six minutes before the half-time shrill.

READ MORE: Manchester United player ratings vs Leicester City as Joshua Zirkzee good but two 3/10s

READ MORE: 'Look on Wyscout' - Manchester United head coach Ruben Amorim hits back at Patrick Dorgu critics

Ruud van Nistelrooy was 22 minutes away from winning as many matches at Old Trafford this season as Ruben Amorim. This was only Amorim's fifth but also his most important.

There were boos, exasperated sighs, supporters snapped at Kobbie Mainoo and there was a command of "Attack, attack, attack". United eventually did.

Appropriately, the winner came via another defender. Harry Maguire has had enough headed chances he should have more goals for United and this one was offside. Alas for Leicester, VAR is not in operation until the fifth round. They will not be in the velvet bag.

United will be. Their season is still salvageable in the cups and there will not be a vacant weekend at the start of March. Their supporters can tune into Monday's draw.

Amorim won’t budge on his formation but did on personnel. United remembered how to attack with Alejandro Garnacho on for the second half. Fellow substitute Joshua Zirkzee equalised and was a crowdpleasing upgrade on his teammates who started.

"How s**t must you be? We're winning away," the Leicester fans sang in the first half. They had only won at Southampton and Tottenham this season, teams that are in United's slipstream.

An hour in, and Leicester fans started 'ole'ing as their team kept the ball with considerable ease. Three minutes later, the Stretford End commanded United to attack, just as the away-dayers had at Fulham 12 days ago. Garnacho and Zirkzee did.

Relieved United fans left hollering Zirkzee's name. He has had significant impacts in the third and fourth rounds of the cup and is emerging as an unlikely cult figure.

United have come full circle again, though. Their stultifying and staid performance in the first hour was reminiscent of the drudgery during Louis van Gaal's second season in 2015-16. Back then, it was commonplace for United not to score in the first half. They have not done so in 12 out of 20 games at Old Trafford this season. There was not a shot on target from United until the 65th minute and Garnacho's eventual strike was deflected.

Left back has been a problem position for United for 18 months, they signed one last week and Amorim played Patrick Dorgu out of position. Dorgu played decently and still only lasted a half. Amorim is overcomplicating matters almost weekly. At least Dorgu's replacement, Garnacho, claimed the man of the match accolade.

This was not a ringing endorsement for the FA Cup. An inconsiderate kick-off time and underwhelming tie, with only a small pocket of away fans present as the majority were priced out by United's avaricious billionaire co-owner.

Van Nistelrooy emerged to a long cry of 'Ruuuuud' and warm applause. He and Amorim clasped hands and exchanged a business-like embrace but did not linger. Casemiro, a starter in all four of Van Nistelrooy's matches as caretaker manager, made a beeline for his old ally in the tunnel and lingered outside the away dressing room. Alas, the transfer window shut on Monday.

The left-footed left back Dorgu peculiarly lined up on the right wing. He was not inhibited by switching to the opposite flank. Dorgu was involved in a breakaway and actually had a shot. Amad offered him encouraging applause after the latter. Then United fans put their hands together for the Dane following a committed header.

And still Dorgu, the only remote positive in a tedious half, was hooked at half-time. Amorim has a blind spot with his compatriot, Diogo Dalot, who played on and out of position.

United players donned training tops with 'Mucha fuerza, Licha!' - 'lots of strength, Licha' printed on the back in tribute to the crushed Martinez. He was immediately missed.

Impatience crept in after 15 minutes, with United supporters demandingl a quicker build-up from the backline. Several vented at Mainoo for a backward pass on 30 minutes when he had the space to carry the ball into the Leicester half. That was his sixth touch.

Mainoo's confidence was at a season-high last week after his influential role in the 2-0 win away to FCSB. Seven days later, it is at a season low. He is discovering, like Marcus Rashford, there is a different level of expectation reserved for United players born in Greater Manchester and Mainoo does not have the support network. He made way for Zirkzee 18 minutes into the second half.

Rasmus Hojlund had the gall to barrack the linesman for flagging him offside. Later in the first half, he apologised to Leny Yoro for misreading a lofted pass. Hojlund was bickering with Bruno Fernandes as late as the 90th minute and also had some verbal sparring with Amorim.

Leicester fans required only one block to access the away section. The inconvenient 8pm start and a third visit to Old Trafford within four months were sufficient deterrents but none more than the obscene £51 cost of a ticket. Come the 93rd minute, it was not worth it.

Then they were out of time.