Ivan Toney converted from the penalty spot in the 24th minute for the only goal of a contest lacking in chances. The Bees move up to 12th in the table while the Toffees drop to 14th. extending their winless run to seven.
Story of the match
The only goal of the match came from a corner. Sergi Canos took it and after the first delivery was cleared, he got another chance and that was punched away by Everton goalkeeper Jordan Pickford.
In between that sequence of events, Lewis Gordon ran nearly the entire length of the field and found Salomon Rondon, who looked set to finish, but Mbeumo made a saving tackle.
Toney stepped up to take the penalty and sent Pickford the wrong way, finishing to the right to put the hosts in front.
The Toffees nearly equalized seconds after the goal. Rondon had the ball at his feet down the left side, turned and fired, but Alvaro Fernandez got down low to save with his feet.
Townsend got to the loose ball and sent in a cross to Rondon, whose header was saved well by Fernandez.
Pickford was on hand to make a spectacular stop after a neat sequence by Brentford. Mbeumo won a header that allowed Toney and Onyeka to exchange passes. Onyeka then sent in a cross that Pickford dove to save with Mbeumo on the doorstep.
With the game being played at a high pace, the Bees settled things down and took control. Toney played a clipped pass to Mbeumo, who snatched at a shot that Pickford easily collected.
Brentford nearly doubled their lead a minute into the second half when Canos met a half-cleared long throw on the volley, but he fired over the crossbar.
The visitors then had a couple of chances when a clearance by Goode was brought down and lashed over by Rondon. Vitaly Janelt then got in a crucial block after Seamus Coleman's cross dropped to Rondon.
The Toffees pushed for a late equalizer as Rondon headed wide and Fernandez again saved from Iwobi.
There was little action in the closing moments of the match as Brentford picked up a much-needed victory while Everton head into the Merseyside derby in extremely poor form.
Man of the match: Alvaro Fernandez
With David Raya expected to be out a bit longer, this was an important performance for the Spaniard. He made five saves, four inside his box and three high claims with his feet being key, as well.