An early attack from the hosts momentarily looked like it would end a run of five home league matches without a goal, but Mark Flekken was equal to Jamie Vardy’s effort after a brilliant jinking run from the 38-year-old.
Any Leicester positivity turned out to be premature though, with Mikkel Damsgaard’s delicate flicked pass cutting through the Foxes to allow Yoane Wissa to sweep a bouncing ball in off the post.
With momentum on their side, Brentford doubled their advantage on 27’ through Mbeumo, who collected the ball on the edge of the box, shifted inside, and bent a strike beyond Mads Hermansen.
The Foxes were looking far from stable at the back, conceding again five minutes later when Christian Nørgaard nodded home from Mbeumo’s set-piece delivery whilst under minimal pressure.
As first-half stoppage time arrived, plenty of home fans had already left the King Power Stadium, missing further distress as Kevin Schade headed onto the post and Keane Lewis-Potter saw his would-be goal ruled out for handball.
Trailing at the break for the eighth PL home match this campaign – the highest tally in the division – Leicester were greeted by a rather flat atmosphere after the restart.
A largely uneventful 20-minute period left the hosts with a mountain to climb and staring at just a second H2H loss in 14 encounters (W9, D3).
With the contest drifting towards its inevitable conclusion, Brentford almost added another goal through substitute Yehor Yarmolyuk, only for Hermansen to produce a fine stop.
That fourth and final goal did eventually arrive when Fábio Carvalho tucked home from close range in the 89th minute following good work from Mbeumo.
The pouring rain perfectly encapsulated the Leicester mood as they ultimately fell to a 10th defeat in 11 PL games, mounting further pressure on boss Ruud van Nistelrooy, who misses the chance to guide his 19th-placed side out of the relegation zone.
Meanwhile, a remarkable turnaround in travelling form has helped lift Thomas Frank’s side into the top half for the time being.