Ralf Rangnick’s side survived a torrid opening 45 minutes, when their performance was laced heavily with mediocrity – as De Gea made key saves from Mathias Jensen and the home side missed other big chances.
It was a different story after the break as United, no doubt fired up by a few well-chosen words from Rangnick, turned up the intensity and the quality to punish Brentford for their profligacy.
Teenager Anthony Elanga headed his first goal of the season from Fred’s pass 10 minutes after the break before Cristiano Ronaldo’s superb chest pass helped Bruno Fernandes set up the second unselfishly for Mason Greenwood.
Ronaldo produced a ridiculous show of petulance with a slow stroll off, some very obvious muttering and a burst of anger on the bench after he was substituted with 20 minutes left.
But Rangnick’s change was fully justified as substitute Marcus Rashford scored with a smooth near-post finish after 77 minutes, with Fernandes the creator again.
Ivan Toney pulled one back in a scramble late on but the damage was done for Brentford when they failed to cash in after carving United open in the first half.
De Gea the difference as Man Utd come good
Manchester United were leaning on a familiar pillar during a shocking first half when Brentford’s pace, energy and direct running threatened on a regular basis.
De Gea was the key figure as United creaked, twice thwarting Jensen when his legs when it looked certain the Bees would take the lead.
It was the only positive in a dismal first 45 minutes from United when they lacked urgency, aggression and any shred of creativity, as they lost challenges and were constantly forced on to the back foot.
United boss Rangnick will have been relieved to get United in at the interval on level terms and no doubt a strong message, and not a complimentary one, was delivered.
To United’s credit, they responded with real vigour and once Elanga put them in front they were always in control, with further goals from Greenwood and Rashford putting the gloss on a much-improved second half.
The sight of Rashford finishing with such efficiency, and Fernandes back in his role of creator, will have lifted Rangnick as United kept on the heels of the top four. They are in seventh place but are only two points behind West Ham in fourth with a game in hand.
Brentford’s big regrets
Brentford will know they only have themselves to blame for a defeat that could have been a victory had they shown a cutting edge in the first half.
Thomas Frank’s side sensed United were vulnerable in the first half and reduced the visitors’ defence to a state of panic at various stages.
Sadly for Brentford, Jensen could not take those opportunities and Brentford’s finishing was wayward on other occasions when they looked like capitalising on their superiority.
As they went in level at half-time, the big fear was that wastefulness would come back to haunt them and so it proved.
There was almost a sense of inevitability that United would punish them and once Elanga broke the deadlock, the hosts could not get back into the game.
Brentford, however, once again looked competitive and comfortable at this level. Their attitude and application could not be faulted. It was only the final product that was missing and they are still in a position in the Premier League they would have gladly settled for at the start of the season.
Ronaldo’s petulance an unnecessary sideshow
Manchester United were well in control when Rangnick decided to remove Ronaldo with 20 minutes left and send on Rashford.
It was hardly controversial but we were treated to the full range of Ronaldo complaints as he walked off at snail’s pace, shaking his head and muttering before having a rather comical struggle with his coat in the dugout.
All in all, this was not a happy Ronaldo as his ego provided a completely unnecessary sideshow to United’s win, which was pretty much sealed by the time he was taken off.
Rangnick was completely unmoved as Ronaldo fumed but was then completely justified in his decision as Rashford finished Brentford off with a lovely near post finish that gave goalkeeper Jonas Lossl no chance.
United’s interim manager leaned over to give the pouting Portuguese what was presumably an explanation for his decision, not that he needed to. Rashford’s goal was explanation enough.
It was a needless exhibition by Ronaldo who, for all his brilliance, still gives off the air of a player and personality who almost thinks he is bigger than Manchester United.
Ronaldo does himself no good with such antics – especially when his manager’s change worked so successfully.