Belgium international Lukaku, who arrived from Everton for a reported £75million, opened his account in the 2-1 friendly win over Real Salt Lake on Monday.
And Lukaku made it two goals in two games with Thursday’s opening strike in the first Manchester derby played on foreign soil at NRG Stadium in Houston, Texas – where Ederson and Kyle Walker made their debuts for City.
Lukaku showed his pace and power as he put United ahead after rounding City’s debutant goalkeeper Ederson – who experienced a mixed evening – in the 37th minute and Pep Guardiola’s men crumbled again before half-time.
Playing with Lukaku for the first time, Marcus Rashford was not overshadowed as he produced a clinical finish to double the lead two minutes later.
Aside from Eric Bailly, Jose Mourinho named arguably his strongest XI, with David de Gea, Antonio Valencia, Victor Lindelof, Chris Smalling, Daley Blind, Ander Herrera, Paul Pogba, Henrikh Mkhitaryan, Jesse Lingard, Rashford and Lukaku in the line-up.
City fans got a glimpse of Ederson and Walker for the first time, while Sergio Aguero, Kevin De Bruyne, Vincent Kompany, Raheem Sterling and Yaya Toure also started, with star recruit Bernardo Silva still away on holiday following the Confederations Cup.
With the worker bee – a symbol of Manchester’s industrial heritage – on United and City’s jerseys in respect to those affected by the terror attack in May, there was added motivation and emotion to the pre-season derby.
Ederson was tested early following his arrival from Portuguese champions Benfica, pushing away Herrera’s long-range effort for a corner, as United looked sharper and quicker on the ball.
Lukaku, Rashford, Mkhitaryan and Lingard were all threatening but you could forgive City for starting sluggishly, this was their first competitive pre-season fixture after all. However, they slowly found their rhythm thanks to 17-year-old Englishman Phil Foden, who showed poise and quality beyond his age.
And there was a tricky moment for De Gea in the 25th minute after Sterling’s shot took a deflection off Smalling – the Spanish goalkeeper scrambling to get a hand to the ball.
United somehow survived going 1-0 down on the half-hour mark after desperately throwing their bodies on the line to block shots from Patrick Roberts and Sterling.
But United went into the break in control thanks to quick-fire goals from Lukaku and Rashford.
Lukaku nodded the ball past the onrushing Ederson and fired brilliantly into the net from an acute angle in the 37th minute.
And City fell apart two minutes later as Mkhitaryan’s penetrating run through the middle created space for Rashford on the left and the youngster finished coolly past Ederson.
It almost got worse for Ederson seven minutes into the second half when the Brazilian was nearly caught off his line by Rashford.
There was another let off for City after Lukaku rattled the woodwork from just inside the penalty area minutes later.
The second half brought an influx of changes as Gabriel Jesus, Leroy Sane, John Stones, Nicolas Otamendi, and even City outcasts Samir Nasri and Eliaquim Mangala were given minutes.
Mourinho also introduced the likes of Anthony Martial, Michael Carrick, Marouane Fellaini and Bailly, and the substitutions took the energy and intensity out of the game as United eventually eased to victory in their ICC opener.