Brentford proved difficult to break down in the opening 45 minutes of an engaging replay but Chelsea improved beyond recognition after the interval as goals from Juan Mata, Oscar, Frank Lampard and John Terry extinguished the League One side's hopes of pulling off the unlikeliest of scalps.
Rafa Benitez gave the competition the respect it deserves in selecting a strong Chelsea XI but it was largely a flat first half performance from the hosts, who started the contest 48 places above their visitors. Brentford kept a solid shape throughout and while only threatening intermittently they grew in confidence as the half progressed, with Chelsea and Lampard in particular left to rue profligacy in front of goal.
The England man twice squandered gilt-edged chances in failing to make a proper connection when well-placed from Branislav Ivanovic right wing deliveries.
The Serbian had earlier gone close himself to breaking the deadlock when a looping header drifted over the top of Bees goalkeeper Simon Moore's far post.
For Brentford it was the industrious and highly-rated Adam Forshaw who looked the likeliest bet for Uwe Rosler's side as two decent strikes had power but lacked precision from range.
The closest either side came to threatening the score-sheet arrived on 25 minutes when Oscar, Chelsea's brightest spark, clipped the outside of the post after being fed in by Mata.
An over eager whistle from Neil Swarbrick angered Brentford's players towards the end of the first period when Marcello Trotta had the ball in Chelsea's net but not before the match official had blown for a foul on Forshaw on the edge of the area.
Presumably with a flea in their ear Chelsea came out for the second half with more purpose as Moore was forced into a smart early stop when he repelled Ivanovic's powerful header from a corner.
There was nothing he could do though in the 54th minute to prevent Chelsea from taking the lead. Petr Cech's long clearance downfield set up an aerial duel won by Demba Ba and, when the ball broke to Mata 20 yards from goal, he set his sights before rifling a trademark daisy cutter past Moore in some style.
It was a lead doubled by Oscar's impudent flick from close range after substitute Eden Hazard had picked off some wasteful Brentford passing to feed-in a marauding Ivanovic, whose cross was beautifully finished by the Brazilian.
Thereafter it was a question of how many Chelsea might score as Lampard bagged himself another club record when his tap-in from Mata's clipped cross, his 199th goal for Chelsea, saw him surpass Bobby Tambling's record for FA Cup strikes on 26.
An almost perfect second half was capped by a Terry goal on his return as he rose at the far post to nod in Oscar's clever looping cross. The only sour note of the afternoon came five minutes from time when David Luiz needlessly crashed into Bees substitute Jake Reeves in a reckless challenge that could have earned him a red card from a less lenient referee.
Chelsea will now play Middlesbrough at The Riverside in the fifth round.
|0||1st Half Goals||0|
|5||Shots on Target||0|
|6||Shots off Target||4|
|72||1st Half Poss.||28|
|59.7||2nd Half Poss.||40.3|