Having seen top-four rivals Tottenham and Aston Villa register wins earlier in the day, United travelled to West London knowing the importance of picking up maximum points.
It was the struggling hosts, however, who edged a closely fought opening half-hour, with Ivan Toney directing their best opportunity against the inside of the post.
Grateful for that reprieve, Erik ten Hag’s side looked to gain a foothold in the match as the first half progressed, but Brentford once again came close to a breakthrough, as Mathias Jørgensen saw an angled header flick the top of the crossbar.
The one-way traffic showed no signs of slowing down with HT approaching, and Yoane Wissa missed another promising opportunity from close range as United made it through to the break unscathed.
The opening stages of the second half followed a similar pattern to the first, but for all their dominance, Brentford were soon indebted to keeper Mark Flekken, who produced a superb reflex save to deny Rasmus Højlund.
United shot-stopper André Onana was just as busy at the opposite end, thwarting Yegor Yarmolyuk and Keane Lewis-Potter with a fine double save before Wissa fired another effort for the hosts against the outside of the post.
Determined to make their pressure count, Brentford thought they’d finally broken the deadlock with 20 minutes remaining, but Toney’s well-taken volley was ruled out for a marginal offside.
Chances continued to flow for the hosts with time ticking into the final quarter-hour, however, substitute Bryan Mbeumo could only direct a powerful strike against the woodwork as the United rearguard held firm under pressure.
Having been on the back foot for almost the entirety of the match, United thought they’d snatched the most unlikely of winners when Mason Mount tucked home to send the travelling support into raptures.
However, in the most remarkable of finishes, Brentford went straight up the other end to hit back in the ninth minute of stoppage time, as Kristoffer Ajer converted from Toney’s clever cut-back, earning a well-deserved point for the Bees.
The result sees Brentford move five points clear of the drop zone, while United lose further ground in the top-four race.
Flashscore Man of the Match: Mathias Jensen (Brentford)
