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.
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. (Courtesy BBC)