Ralf Rangnick's aspect had been indebted to David de Gea for a superb first-half display that kept Brentford at bay earlier than United finally sprang to life in west London.
Anthony Elanga positioned United in the front early inside the 2nd 1/2 before Mason Greenwood and Marcus Rashford wrapped up the factors.
United are the first club to report three hundred Premier League away victories despite Brentford's late reply from Ivan Toney.
They take a seat seventh within the table, two points adrift of the pinnacle 4 as they chase qualification for next season's Champions League.
But it was Ronaldo's grumpy response to Rangnick's decision to haul him off in the 71st minute that might show the night's lasting photo.
Shaking his head and muttering to himself, Ronaldo seemed to mention something to Rangnick as he brushed beyond him.
Angrily throwing his coat to the ground, Ronaldo pointed at his chest while his crew-friends at the bench nervously regarded away.
Rangnick first of all ignored Ronaldo before sitting next to him and patting the Portugal ahead on the leg as he tried to placate him.
The 36-yr-vintage's strop will boost clean questions about his willingness to match into Rangnick's device after his modern underwhelming display.
United as a minimum avoided every other embarrassing result after dropping at home to Wolves and letting a -goal lead slip in a draw at Aston Villa of their previous two league video games.
