Story of the match
Chelsea were on the front foot in the opening stages of the match as Ruben Loftus-Cheek was able to weave through some space and Timo Werner got in the penalty area, but Mathias Jensen made a timely tackle and the danger was averted.
Despite that, the Blues created very little during the first half-hour of the match, Romelu Lukaku lashing a free-kick over the most notable action in that period.
Brentford's first chance came when they worked a long throw short and Mathias Jorgensen delivered a cross that was met by Ivan Toney, but his header was deflected wide.
The subsequent corner was only cleared as far as Sergi Canos and his cross to the far post found Ethan Pinnock whose header was nodded on by Christian Norgaard into the path of Bryan Mbuemo, but he hit the post with his shot.
Chelsea thought they had opened the scoring after Werner found Lukaku with a cross that beat David Raya, but the assistant referee's flag went up for offsides and a VAR review confirmed the call.
After both teams nearly scored, the visitors did have the ball in the back of the net when N'Golo Kante crossed for Cesar Azpilicueta and after it was only half-cleared, Chilwell beat Raya from the edge of the area.
The Blues pushed for a second shortly after the interval as Mateo Kovacic got on to a half-cleared corner but blasted it over the top. Pinnock blocked Werner's shot and Lukaku smashed over in an offside position.
It was almost all undone when Henry found Canós from a half-cleared corner. The Spaniard chipped a cross to the far post and it took a header at full stretch from Malang Sarr to see off the danger.
Brentford continued to attack as they searched for the equalizer, Pinnock flicking a long throw into the path of Toney, a brilliant save by Edouard Mendy denying him.
Nørgaard then fed substitute Marcus Forss and he sent it to Mbuemo, but he hit the woodwork, the second time the post denied the Bees. Over the final ten minutes, Forss and Saman Ghoddos saw shots blocked.
Mendy proved to be the difference as he denied Pontus Jansson, Ghoddos had another effort blocked and the Chelsea goalkeeper stymied Nørgaard as the Blues earned a hard-fought victory.
Man of the match: Edouard Mendy
He was sensational, especially in the second half as Brentford pushed for an equalizer, making several key saves to keep the Bees off the board and earn Chelsea all three points.