Xherdan Shaqiri came off the bench to inspire a Liverpool victory over a lacklustre Manchester United that takes them back to the top of the Premier League.
Liverpool needed the win after Manchester City beat Everton on Saturday - and it was substituted Shaqiri's rapid-fire double strike in the second half that gave Jurgen Klopp's side the three points they fully deserved.
Sadio Mane's 24th-minute volley from Fabinho's perfect delivery gave Liverpool the lead their lightning start merited, only for a dreadful error by goalkeeper Alisson to give United an unlikely lifeline before the break when he fumbled Romelu Lukaku's cross into the path of Jesse Lingard.
United barely offered an attacking threat but were frustrating Liverpool until Klopp introduced Shaqiri with less than 20 minutes remaining, with devastating effect.
Meanwhile, Paul Pogba remained an unused substitute on United's bench, Jose Mourinho opting instead to bring on Marouane Fellaini at the interval with his side short of inspiration.
There was an element of good fortune about both of the Swiss international's goals, one deflected in from close range and the other off Eric Bailly to beat keeper David de Gea - but one cannot begrudge Liverpool their victory against this desperately ordinary United side.
Liverpool and Klopp faced a pivotal week in their season that would shape the immediate future - and they answered the questions posed of them in emphatic fashion.
The two tasks in hand were to get the victory they needed over Napoli to reach the last 16 of the Champions League then beat Manchester United to return to the Premier League summit.
Liverpool showed no hangover from their midweek efforts in successfully achieving that Champions League mission as they set about United with relish and went ahead through Mane - although Alisson's gift to Lingard stopped their momentum and gave Mourinho's side a chance of the point that seemed to be the extent of their ambitions.
Shaqiri's introduction changed all that to leave Klopp's men still unbeaten in the league and United 19 points adrift of their arch-rivals.
Liverpool are currently in the sort of mood where they believe anything is possible and the signing of Shaqiri has added to their collection of match-winners.
Mohamed Salah was quiet but Shaqiri stepped up in an impressive demonstration of the squad strength at Klopp's disposal.
Manchester United and manager Mourinho may point to the two decisive deflections on Shaqiri's goals - but they would be fooling only themselves if they believe they deserved anything from this game.
Mourinho's gameplan, predictably, was one of physical strength and containment that Liverpool were dealing with dismissively until Alisson's blunder threw them off their stride.
The Old Trafford boss added further physical power in the shape of Fellaini at half-time but it was still Liverpool, albeit nowhere near as impressively as in the first period, who were positive and pushing, while United were passive.
Pogba was not even used and Anthony Martial arrived when it was too late - while Klopp brought on the maverick game-changer Shaqiri to make the difference.
The contrast was almost symbolic, demonstrating just how quickly United are heading in the opposite direction to this vibrant Liverpool side.