Ole Gunnar Solskjaer was the ultimate supersub for Manchester United - but even he never scored within two seconds of his introduction.
That is what Romelu Lukaku did here to set up a victory which sees his manager become only the second in the club's history to win their first four league games in charge. Sir Matt Busby is the other, and that's not bad company to keep a few weeks into the job.
Lukaku needed just two minutes to score after coming on during Sunday's 4-1 victory over Bournemouth. But he wasn't hanging around this time.
Marcus Rashford slips the ball home after being played in by Alexis Sanchez for Manchester United's second goal
Rashford celebrates after making sure of the points and a fourth win in four under interim boss Ole Gunnar Solskjaer
Romelu Lukaku is alive to the situation after Martin Dubravka failed to hold onto Marcus Rashford's free-kick
The Belgian striker celebrates after scoring with his first touch just 38 seconds after coming on as a substitute
Victor Lindelof, Ander Herrera, Alexis Sanchez and Marcus Rashford celebrate with the goalscorer Lukaku
Newcastle defender DeAndre Yedlin consoles Martin Dubravka after his error let Manchester United break the deadlock
Newcastle: Dubravka, Yedlin, Schar (Muto 81), Lascelles, Dummett, Ritchie, Diame (Shelvey 53), Hayden, Atsu, Perez (Kenedy 69), Rondon
Subs not used: Woodman, Manquillo, Lejeune, Joselu
Manchester United: de Gea, Valencia, Lindelof, Jones, Shaw, Herrera, Matic, Pogba, Mata (Sanchez 63), Rashford (Lingard 87), Martial (Lukaku 63)
Subs not used: Romero, Darmian, Young, Fred
Goalscorers: Lukaku 64, Rashford 80
Booked: Lindelof, Shaw
Referee: Andre Marriner
Marcus Rashford completes a flowing counter-attack to finish for the game for Manchester United. CLICK HERE for more from MATCH ZONE.
The Belgian had watched for 64 minutes as his team-mates toiled, a shadow of the side who had smashed 12 goals in three games since being freed of Jose Mourinho's smothering and impeding presence.
United had a free-kick 25 yards from goal as Lukaku - joined by fellow sub Alexis Sanchez - trotted into position.
Marcus Rashford took aim and, when his dipping effort bounced just in front of Martin Dubravka, Lukaku pounced to take advantage of the goalkeeper's spill.
It was a relief for Solksjaer - whose team had been second best until that point against Rafa Benitez's Magpies - and Sanchez laid on the game-clinching second for Rashford 10 minutes from time.
Benitez has long since been criticised for the negative tactics he employs against the top clubs. His argument has always been that he is managing the meagre resource available to him, and he has a point given the club have returned a £2million profit over the last three transfer windows.
Yet here was a first-half performance in which they matched the visitors, even bettering them in terms of chances created.
Newcastle fans unfurled a banner ahead of kick-off at St James' Park taking aim at their opponents on Wednesday night
Alexis Sanchez was back on the bench at St James' Park having last featured in the Manchester derby on November 11
Manchester United midfielder Paul Pogba attempts to shrug off the attentions of Newcastle's Isaac Hayden
Newcastle defender Paul Dummett gets his toe to the ball to win it ahead of Manchester United striker Marcus Rashford
Paul Dummett keeps his eyes on the ball as Manchester United playmaker Juan Mata aims to reach it first
Manchester United's interim manager Ole Gunnar Solskjaer tries to get his point across from the touchline
The inclusion of Phil Jones at centre-back for United as replacement for the suspended Eric Bailly had perhaps given the hosts hope and, rather than attempt to knit pretty patterns around the