Lukaku has right stuff for United
made it easier for themselves but Anthony Martial lifted a sitter over the bar midway through the second half.
He was hooked by Mourinho shortly after and his replacement Marcus Rashford was unlucky not to score when his drive struck the bar.
Bournemouth sensed that United might be vulnerable early on and the pace of Josh King caused his former club some anxiety with Phil Jones having to get in vital challenges and blocks on three occasions.
United looked anxious and twice needed De Gea to produce saves, the first when Charlie Daniels burst forward and unleashed a skidding 25-yard shot and then when Dan Gosling fired in a goalbound shot from a tight angle. United had barely threatened as an attacking force when they took the lead against the run of play.
Martial made a run down the left before turning the ball back to Mata, who crossed to the far post where Lukaku was too strong for Ake as he powered a header past Asmir Begovic and into the top corner.
It did not deter Bournemouth. De Gea was brought into action again by Junior Stanilas’ low drive while skipper Simon Francis missed the best chance of the first half when, unmarked, he fired high into the Stretford End after a corner dropped to him eight yards out.
Lukaku was booked for a foul on Harry Arter and was relieved that referee Graham Scott had not cautioned him for an earlier challenge on Ake, otherwise his night would have been over.
Just before the break De Gea had to react smartly to stop Ryan Fraser’s cross-shot from sneaking in at his near post and the Cherries could feel aggrieved to be behind at half-time.
United endured an anxious second half. They needed a second goal to kill off Bournemouth but Martial turned the ball over the top when it looked easier to score after Begovic had saved Lukaku’s shot.
Rashford’s piledriver came back off the bar with Begovic beaten but United needed De Gea to rescue them when Jermain Defoe had a late chance.
MAN UTD (4-2-3-1): Booked: NEXT UP: BOURNEMOUTH (4-4-1-1): Booked: Goal: