Frank Lampard's goal against Brentford was his 26th in the FA Cup as he became Chelsea's leading scorer in the competition, surpassing Bobby Tambling. Lampard now has 199 goals in total for the Blues.
Chelsea dominated the first half but despite several chances they failed to break the deadlock.
Oscar was their most lively threat with the Brazilian scuffing against the post while earlier seeing his goal-bound shot deflected over the bar by Harlee Dean.
Branislav Ivanovic also went close for the Blues, heading Mata's free-kick back across goal and wide while Lampard was unusually inaccurate in front of goal after volleying erratically wide from 10 yards.
Adam Forshaw was Brentford's best attacking threat with the midfielder sending two efforts from distance wide of Petr Cech's goal.
Forshaw was threatening again when David Luiz sent him crashing to the turf on the edge of the penalty area, winning a free-kick that infuriated Brentford as Marcello Trotta had rifled his shot past Cech just as the whistle blew for a foul.
Chelsea started the second half with more urgency and Ivanovic forced an excellent low save from Simon Moore with his close-range header from Oscar's cross.
The holders were eventually ahead and it came from their top scorer this season with Mata finding the net with a low strike from 20 yards after Ba's knockdown from Cech's long punt.
Brentford pressed for an equaliser but struggled to break down a well-organised Chelsea defence and it was the hosts who scored next doubling their lead through Oscar's flick from Ivanovic's cross that was deflected past Moore.
Clayton Donaldson headed over for the Bees moments later but the tie was all but sealed as Lampard scored Chelsea's third.
In doing so Lampard became Chelsea's all-time goalscorer in the FA Cup with his 26th in the competition, also taking his tally to 199 goals for the Blues as he side-footed Mata's cross past Moore from 10 yards out.
Terry completed the rout with a late header following a fine, incisive cross from Oscar.
In the closing moments, Luiz was lucky to escape punishment after a cynical shoulder barge on Jake Reeves as the game, that had been played in right spirit, ended on a sour note.
Full Time The referee blows his whistle to end the game.
Eden Hazard decides to take the corner short.
Harry Forrester takes the inswinging corner, Demba Ba manages to make a clearance.
A cross is delivered by Harry Forrester, clearance by David Luiz.
Foul by Clayton Donaldson on John Terry, free kick awarded. Petr Cech restarts play with the free kick.
Yossi Benayoun challenges Tom Adeyemi unfairly and gives away a free kick. Direct free kick taken by Sam Saunders.
Free kick awarded for a foul by Jonathan Douglas on Branislav Ivanovic. Direct free kick taken by Petr Cech.
Harlee Dean takes the direct free kick.
Booking David Luiz receives a yellow card.
Free kick awarded for a foul by David Luiz on Jake Reeves.
The assist for the goal came from Emboaba Oscar.
80:46 Goal scored
Goal! - John Terry - Chelsea 4 - 0 Brentford John Terry finds the back of the net with a headed goal from inside the six-yard box. Chelsea 4-0 Brentford.
Emboaba Oscar sends in a cross,
Emboaba Oscar takes a short corner.
Substitution Ryan Bertrand on for Frank Lampard.
Substitution Sam Saunders joins the action as a substitute, replacing Adam Forshaw.
Substitution Juan Mata goes off and Yossi Benayoun comes on.
The ball is crossed by Jake Bidwell, comfortable save by Petr Cech.
Substitution Jake Reeves joins the action as a substitute, replacing Toumani Diagouraga.
Assist by Juan Mata.
70:53 Goal scored
Goal! - Frank Lampard - Chelsea 3 - 0 Brentford Frank Lampard fires in a goal from inside the six-yard box low into the middle of the goal. Chelsea 3-0 Brentford.
Corner taken by Harry Forrester, Clayton Donaldson has a header from deep inside the six-yard box and clears the crossbar.
Jake Bidwell crosses the ball in from the free kick, clearance made by Gary Cahill.
Booking Branislav Ivanovic shown a yellow card.
Free kick awarded for an unfair challenge on Harry Forrester by Branislav Ivanovic.
Branislav Ivanovic provided the assist for the goal.
67:38 Goal scored
Goal! - Emboaba Oscar - Chelsea 2 - 0 Brentford Emboaba Oscar finds the back of the net with a goal from close in low into the middle of the goal. Chelsea 2-0 Brentford.
Branislav Ivanovic produces a cross,
Free kick taken by John Terry.
Substitution Victor Moses goes off and Eden Hazard comes on.
Free kick awarded for an unfair challenge on Juan Mata by Shaleum Logan.
Frank Lampard gives away a free kick for an unfair challenge on Tom Adeyemi. The free kick is swung in right-footed by Adam Forshaw, clearance made by Gary Cahill.
The assistant referee signals for offside against Clayton Donaldson. Indirect free kick taken by Petr Cech.
The official flags Demba Ba offside. Free kick taken by Harlee Dean.
Corner taken left-footed by Juan Mata from the left by-line, Gary Cahill takes a shot. Blocked by Tony Craig.
The ball is delivered by Juan Mata, Jonathan Douglas gets a block in.
David Luiz concedes a free kick for a foul on Harry Forrester. Harry Forrester takes the free kick.
Outswinging corner taken by Adam Forshaw.
Free kick awarded for an unfair challenge on Harry Forrester by David Luiz. Jake Bidwell delivers the ball from the free kick left-footed from left wing, Frank Lampard manages to make a clearance.
Clayton Donaldson crosses the ball.
Substitution Harry Forrester is brought on as a substitute for Marcello Trotta.
53:55 Goal scored
Goal! - Juan Mata - Chelsea 1 - 0 Brentford A goal is scored by Juan Mata from outside the area to the bottom right corner of the goal. Chelsea 1-0 Brentford.
Foul by Toumani Diagouraga on Victor Moses, free kick awarded. David Luiz takes the direct free kick.
Gary Cahill takes a shot. Jonathan Douglas gets a block in.
Juan Mata crosses the ball, Harlee Dean makes a clearance.
Outswinging corner taken right-footed by Emboaba Oscar from the right by-line, clearance by Jonathan Douglas.
Victor Moses delivers the ball, blocked by Toumani Diagouraga.
Ashley Cole fouled by Adam Forshaw, the ref awards a free kick. Juan Mata crosses the ball in from the free kick, Toumani Diagouraga manages to make a clearance.
The ball is crossed by Emboaba Oscar, Branislav Ivanovic takes a shot. Save made by Simon Moore.
Juan Mata delivers a pass corner to short, Simon Moore makes a save.
The referee starts the second half.
45:00 +1:19 Half time
Half Time The match has reached half-time.
Unfair challenge on Branislav Ivanovic by Clayton Donaldson results in a free kick. Petr Cech takes the free kick.
Corner from the left by-line taken by Adam Forshaw, clearance made by Demba Ba.
The ball is swung over by Clayton Donaldson, Tom Adeyemi takes a shot. Blocked by John Terry.
The ball is delivered by Branislav Ivanovic, Frank Lampard produces a right-footed shot from close range which goes wide of the left-hand upright.
Marcello Trotta is ruled offside. Petr Cech takes the indirect free kick.
The ball is crossed by Jake Bidwell.
Free kick awarded for an unfair challenge on Toumani Diagouraga by Emboaba Oscar. Direct free kick taken by Simon Moore.
David Luiz concedes a free kick for a foul on Adam Forshaw. Shot on goal comes in from Adam Forshaw from the free kick. Adam Forshaw takes a shot. David Luiz gets a block in.
Free kick awarded for an unfair challenge on Ashley Cole by Shaleum Logan. Frank Lampard produces a shot on goal direct from the free kick, Clayton Donaldson makes a clearance.
Unfair challenge on David Luiz by Jonathan Douglas results in a free kick. Gary Cahill takes the direct free kick.
The offside flag is raised against Emboaba Oscar. Indirect free kick taken by Simon Moore.
Foul by Harlee Dean on Demba Ba, free kick awarded. David Luiz takes the direct free kick.
Effort from outside the box by Adam Forshaw goes wide right of the target.
David Luiz sends in a cross, save by Simon Moore.
Foul by Harlee Dean on Demba Ba, free kick awarded. Juan Mata crosses the ball in from the free kick, Marcello Trotta makes a clearance.
Shot by Emboaba Oscar from inside the box bounces off the post.
The ball is sent over by Juan Mata. The ball is crossed by Ashley Cole.
Frank Lampard has an effort at goal from outside the box which goes wide right of the goal.
Centre by David Luiz, Tony Craig manages to make a clearance.
Ashley Cole sends in a cross, Emboaba Oscar takes a shot. Blocked by Jonathan Douglas.
Centre by Jake Bidwell. Adam Forshaw takes a shot.
The ball is crossed by Victor Moses, Shot from 6 yards by Frank Lampard. Emboaba Oscar takes a shot. Harlee Dean gets a block in. Inswinging corner taken by Emboaba Oscar, clearance made by Jonathan Douglas. Shot from just outside the box by David Luiz goes over the bar.
Emboaba Oscar sends in a cross, Headed effort from inside the area by Demba Ba misses to the left of the goal.
Inswinging corner taken from the right by-line by Juan Mata.
The ball is sent over by Branislav Ivanovic, blocked by Clayton Donaldson.
Free kick awarded for an unfair challenge on Gary Cahill by Jonathan Douglas. David Luiz takes the free kick.
Branislav Ivanovic produces a cross, clearance made by Tony Craig.
The ball is sent over by Shaleum Logan, Clayton Donaldson has a headed effort at goal from deep inside the area missing to the left of the target.
Victor Moses fouled by Jake Bidwell, the ref awards a free kick. The ball is swung over by Juan Mata, Close range headed effort by Branislav Ivanovic misses to the right of the goal.
Adam Forshaw has an effort at goal from outside the penalty box missing to the wide left of the goal.
The offside flag is raised against Tom Adeyemi. Ashley Cole takes the indirect free kick.
Demba Ba takes a shot. Blocked by Tony Craig.
The ball is sent over by Emboaba Oscar, save by Simon Moore.
Free kick awarded for a foul by Jake Bidwell on Victor Moses. Branislav Ivanovic takes the direct free kick.
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