The hosts struggled to break Uwe Rosler's men down in a goalless first half but the floodgates opened in the second, with Oscar, Frank Lampard and John Terry also scoring
After a goalless first half, Juan Mata broke the deadlock before Oscar and Frank Lampard hit a one-two punch midway through the second period and John Terry wrapped it up.
The skipper had been recalled to the starting XI after injury while Victor Moses returned to the fold following his Afcon triumph. Fernando Torres’s replay-earning strike at Griffin Park did not stop him being dropped for Demba Ba while Harry Forrester was unexpectedly benched by Brentford.
The game began evenly and the visitors, far from overawed, had chances early on, with Adam Forshaw’s long shot and Clayton Donaldson’s header wide.
Chelsea had their own efforts but were lucky not to lose a man when Gary Cahill clumsily caught Jonathan Douglas on the shin.
Lampard's shooting boots were askew throughout the first half, mishitting on the edge of the area after 17 minutes before Oscar lifted a scrambled follow-up over.
Using increasingly adventurous passing to open up space, the Blues came closer on 26 minutes, Oscar shooting on the slide when Brentford were caught out but the Brazilian, unable to control the shot, hit the post.
Uwe Rosler’s men kept their heads, however, the impressive Forshaw firing just past Petr Cech’s post. The Bees were later frustrated when Marcello Trotta put the ball in the Blues’ net but referee Neil Swarbrick pulled play back for a David Luiz foul earlier in the move.
With frustration creeping in, Chelsea should have taken the lead just before the break when Mata’s cross found Lampard in space in the box. The midfielder’s touch was clunking, though, and no threat.
After half-time, the Blues continued to press, with Bees keeper Simon Moore reacting superbly to divert Branislav Ivanovic’s header from goal and out of Ba’s reach.
The resistance broke five minutes later, however, when a long ball dropped to Mata. With bodies between him and the goalkeeper, the Spaniard shot across into the far corner and put home hearts at ease.
Brentford plugged away but struggled for venom despite Forrester’s introduction and were broken decisively with 20 minutes to go.
Substitute Eden Hazard held the ball up while Ivanovic overlapped, the Serbian then crossing low into the box where Oscar flicked towards goal. The finish evaded Moore but Harlee Dean inexplicably stepped over it as it rolled over the line.
The sucker-punch followed as Mata ran into space on the left before pulling it back with class for Lampard on the edge of the box, the midfielder this time making no mistake.
With the Bees beaten and the mood calm, captain Terry had freedom to get forward and he nodded in a fourth from Oscar's cross to mark his first-team return.
There was still time for Luiz to get into trouble as he cynically crashed into substitute Jake Reeves, forcing the youngster off for treatment with a challenge that might have warranted more than just a yellow card.