Liverpool breathed new life into their bid for a top-four finish in the Premier League after a 4-2 victory in their rescheduled game at Manchester United.
The initial match on May 2 was called off as anti-Glazer protestors invaded Old Trafford, while Ole Gunnar Solskjaer's team were stuck at the team hotel. United fans again protested outside the ground against the Glazer family ahead of kick-off on Thursday night, but there were no repeats of the scenes of earlier this month.
With both teams safely inside the ground, focus could turn to events on the pitch and United took an early lead when Bruno Fernandes' shot was deflected into his own net by Nat Phillips.
However, Liverpool, who also had a penalty overturned after a pitchside review by referee Anthony Taylor, responded brilliantly as Diogo Jota's flick (34) brought them level before Roberto Firmino's header (45+3) completed the turnaround just before half-time.
Jurgen Klopp's side extended their lead immediately after the restart as Firmino added his second of the night (47), taking advantage of what Gary Neville described as "erratic defending" from a United defence missing the injured Harry Maguire.
The lack of Harry Maguire's presence in the Man Utd defence is obvious for all to see. People question how good is Maguire but you only see it when he is not playing.
Liverpool had chances to finish the game off, but Jota's shot hit the woodwork before United got back into the game as Marcus Rashford's 50th goal at Old Trafford set up a grandstand finish.
Substitute Mason Greenwood saw a shot cleared off the line by Phillips as United searched for an equaliser, but Mohamed Salah's late strike (90) secured the win that sees them move four points off fourth with a game in hand, piling the pressure on Chelsea and Leicester in the race to qualify for next season's Champions League.
The race for the top four...
Protests again at Old Trafford: What happened?
Pictures emerged of the United team arriving at Old Trafford early on Thursday afternoon in a bid to avoid more disruption, but Jurgen Klopp's men may have had their route interrupted.
Images on social media showed a Liverpool-branded bus blocked in by cars near their hotel. Tyres on the coach are reported to have been let down before police arrived.
The bus was on the move at 6pm, when supporters began their anti-Glazer demonstration outside Old Trafford. Fans moved from the forecourt outside the East Stand around the perimeter to the entrance, where the Liverpool team coach would arrive. Police formed a barrier to stop fans on Wharfside Way getting any closer.
The stadium was locked down temporarily, but the Liverpool team was able to arrive.
How Liverpool secured a first win at Old Trafford for Jurgen Klopp...
Finally, after all the talk and 11 days later than planned, we had a game and there were early chances at both ends.
Liverpool's appeals for a penalty were turned down by referee Taylor after Firmino's early cutback hit Eric Bailly's arm, while Alisson Becker's wayward pass almost gifted Edinson Cavani a fifth-minute opener.
However, Liverpool did fall behind in the 10th minute. A swift United move started as Paul Pogba swept the ball into the path of Rashford, who played it onto the overlapping Aaron Wan-Bissaka. The full-back's cutback found Fernandes, whose shot was deflected into his own net by defender Phillips.
The visitors thought they had earned the chance to respond midway through the first half as Taylor pointed to the spot after Bailly's strong challenge on Phillips in the box. But the VAR recommended a pitchside review, and the initial decision was overturned as Bailly was adjudged to have won the ball before catching Phillips with his follow-through.
Man Utd: Henderson (6), Wan-Bissaka (6), Lindelof (5), Bailly (5), Shaw (5), Fred (5), Pogba (6), McTominay (6), Fernandes (6), Rashford (6), Cavani (5)
Subs: Greenwood (7), Matic (5)
Liverpool: Alisson (6), Alexander-Arnold (9), Phillips (8), R Williams (7), Robertson (7), Thiago (7), Fabinho (7), Wijnaldum (7), Salah (8), Jota (8), Firmino (9)
Subs: Mane (6), Jones (6), Williams (6)
Man of the match: Trent Alexander-Arnold
The decision left Liverpool frustrated but they were celebrating moments later.
Dean Henderson had to be alert to keep out Jota's powerful drive, but the hosts failed to deal with the resultant corner. Phillips was involved again as he kept the ball alive after Salah's initial shot was blocked, sending a low ball towards goal and Jota was on hand to flick the ball home from close range.
Liverpool, buoyed by the goal, were starting to dominate and their turnaround was complete just before the break. Trent Alexander-Arnold's inch-perfect free-kick picked out Firmino, who got in behind Pogba at the far post to head home in the third minute of stoppage time.
It took Klopp's men just 72 seconds to extend their lead in the second half after a catalogue of errors from United. It looked like they had got away with Fred's loose pass before Luke Shaw was caught in possession just outside his own penalty area. Henderson then spilled Alexander-Arnold's initial shot before Firmino pounced on the rebound to give the visitors a two-goal advantage.
Jota should have added a fourth just before the hour mark as Liverpool capitalised on another loose Fred pass, but the Portugal international's shot crashed back off the upright.
Alexander-Arnold's low drive was then well saved by Henderson before United got themselves back into the contest.
- Manchester United boss Ole Gunnar Solskjaer made 10 changes once again. Having made 10 alterations for Tuesday's 2-1 loss to Leicester, the Norwegian plumped for the same number on Thursday evening with Eric Bailly the only player to retain his place.
- Roberto Firmino replaced Sadio Mane in Liverpool's only change at Old Trafford.
Cavani played in Rashford and the England forward sent a low shot past the onrushing Alisson and into the bottom right-hand corner.
United had grabbed back the momentum and they were inches away from an equaliser as Phillips cleared Greenwood's volley off the line.
However, as United pushed forward they left acres of space at the back and Liverpool eventually capitalised, Salah coolly finishing past Henderson to put the finishing touch on a late breakaway and seal what could prove to be a vital three points if Liverpool are to qualify for next season's Champions League.
This is a massive win for Liverpool. It's now fully in their hands for the Champions League positions. There's still a lot of work to do but there will be a lot of nerves at Leicester and Stamford Bridge now.
'Good signs for Liverpool' - What the pundits said...
Roy Keane: "Liverpool's attacking play was excellent, they were open at the back but the good sign for Liverpool was they scored four tonight, they should have scored six or seven but missed some easy chances. United were all over the place, poor performance from them, poor mentality, but credit to Liverpool - attacking-wise, they were almost back to their best."
Graeme Souness: "It was a super game, it really was. I'm delighted Liverpool won but Manchester United played their part too. They started really well, for 20 minutes they were dominant, got their goal, Liverpool got themselves going halfway through the half, they were dominant for a good hour.
"Even when United got it back to 3-2, I thought they weathered that pressure and thoroughly deserved to win the game. At 3-1, it could easily have been 4 or 5-1. Liverpool were nearly back to where they were, and there were periods in the game where Manchester United played well too."
Jamie Redknapp: "They're capable of scoring goals, they've shown that today, but the fixtures they've got, they're winnable. If they can get some goals and hope Spurs do them a favour, all you can ask for is a performance like today.
"We've questioned the mindset of the players but they've shown they're good professionals, they got on with it. I thought the front three, minus Mane, with Jota coming in, looked really good today. We've questioned the goals this year, not enough attacking threat, but Trent was good at right-back, it was a really impressive performance."
What the managers said…
Man Utd boss Ole Gunnar Solskjaer: "They deserved the win. We conceded goals in key moments of the game, just before half-time, just after the second half started and of course towards the end. We didn't build on our momentum or break up their momentum. We gave them three goals, really. We scored again and we had momentum, we had a massive double chance, but key moments went against us.
"Their shape and their pressing is very good but we created our own downfall."
On Maguire's absence: "Harry's been really important for us. He's been absolutely top since he came to the club. So of course we're going to miss him. But he's out so we've got to deal with that. We've got good enough players to be able to deal with it. So now it's about regrouping and starting to build our confidence and momentum again.
"The attitude was right, the focus was right. I saw in the boys that we were ready for it, but key moments went against us and we didn't build on the good times we had in the game. We need to find ourselves straight away. We've got Fulham on Tuesday. We don't have a lot of preparation time but we should go into that final ready because I expect Tuesday will be a good one."
Liverpool boss Jurgen Klopp: "Great fight, good game, intense, as all derbies should be. Our first win at Old Trafford since I'm at Liverpool and good timing, I would say. We needed it, obviously. We fought hard for it and we deserved it.
"There were only good performances, to be honest. You saw that our two centre-halves were shaking a little bit at the beginning of the game, you could see it with their passing, but from the moment when they were in the game, when they forgot everything around them, they played really well.
"We are still in the race. That's all we could have done tonight. We did that and now we have a very intense period, with three games in a week. So, in three days, West Brom, which is tough, then Burnley with supporters and Crystal Palace at home. It's very intense. We have to recover quickly and then go again."
Man of the match - Trent Alexander-Arnold
Opta stats - Man Utd's set-piece problem
Manchester United have lost two home games in the space of three days for the first time since April 1958.
Thirty-three per cent of Manchester United's Premier League goals conceded this season have been from set-piece situations (14/42, excluding penalties), the highest ratio in the division.
This was Liverpool's first Premier League win at Old Trafford since March 2014, while it was manager Jurgen Klopp's first away win against Manchester United with the club.
Liverpool are unbeaten in seven Premier League games (W5 D2), the longest current run without defeat in the competition. The Reds had lost six of their seven league games prior to this run.
Live Renault Super Sunday
Liverpool are back in action on Sunday when they travel to West Brom, live on Sky Sports; kick-off 4.30pm.
Meanwhile, Manchester United's Premier League campaign continues next Tuesday when they host Fulham, live on Sky Sports; kick off 6pm.