Juan Mata fired a clinical opening goal after 54 minutes and Oscar, who hit the outside of a post in the first half, tucked in his second goal in four days after 68 minutes.
Mata was the provider for Lampard's 199th Chelsea goal before Terry headed in an 81st-minute fourth as last season's Champions League winners stayed on course for a fifth FA Cup triumph in seven seasons.
After a troubled spell of three wins in 10 games, interim boss Rafael Benitez has now steered the Blues to three successive victories.
The Spaniard is yet to silence his numerous doubters in the Chelsea support, though.
There were reminders of Chelsea's managerial past throughout; the 16th-minute ovation for Roberto Di Matteo and another former Blues boss present in Avram Grant.
Benitez will likely be reminded of Di Matteo up to the clash with Middlesbrough on February 27 following the Italian's 1997 Wembley goal against the Teessiders.
Terry has been said to exert more influence than any of those occupying the place on the bench reserved for the manager, but Chelsea before kick-off vehemently denied suggestions of a recent bust-up between Benitez and the captain.
Terry has been troubled by a knee injury since November and five times he has been an unused substitute under the Spaniard, including for Thursday's 1-0 Europa League win at Sparta Prague.
The 32-year-old made just his third start under the interim boss as one of six changes, while Brentford made three alterations to the side which beat Stevenage, but began with Harry Forrester, who scored in the original tie at Griffin Park, on the bench.
The visitors had the first effort on goal as Adam Forshaw shot wide across Petr Cech before Bees captain Jonathan Douglas tried to spark an attack and was caught on the ankle by a late and high tackle by Gary Cahill.
Victor Moses, returning following his role in Nigeria's African Nations Cup win, was lively for Chelsea and darted round on the right before pulling a ball back for Lampard, who mis-kicked in a crowded area. A follow-up Oscar effort was blocked.
Lampard, who could be months away from leaving the club, then sliced an effort wide. And a Mata cross from the right was just beyond the outstretched leg of Demba Ba, who was playing wearing a protective mask following the broken nose he sustained at Newcastle.
Oscar then struck the post after 26 minutes following flicks from Moses and Mata.
It was not all Chelsea, though, and after a David Luiz cross skipped under Ba's foot, Brentford's counter-attack ended when Forshaw shot narrowly wide from the edge of the area.
Marcello Trotta had the ball in Chelsea's net after 39 minutes, but referee Neil Swarbrick had already blown for a Luiz foul on Forshaw, whose subsequent free-kick hit the wall.
Chelsea should have gone in front when Branislav Ivanovic found an unmarked Lampard in the box, but again the midfielder's usually-clinical finish deserted him.
Fernando Torres spent the match sidelined as an unused substitute, but he was not entirely ignored.
"We want Torres" came the chants from the visiting support as the off-form Spaniard warmed up in front of them, even knowing his only strike in his last 13 appearances came at Griffin Park seven minutes from time which forced the replay.
Time and again Benitez has defended his compatriot, who served him so well at Liverpool, while insisting the January arrival of Ba would aid Torres' cause.
Ba was unable to convert after Simon Moore saved Ivanovic's header from Oscar's cross as Chelsea resumed at pace and on the attack.
It was the direct route which produced a result as Ba challenged Harlee Dean to meet Cech's long clearance and the ball fell for Mata, whose drilled a left-footed shot into the bottom right corner from 20 yards.
Forrester replaced Trotta immediately following the goal and Brentford looked to the winger to produce something.
Supply was in short demand as Chelsea continued to dominate possession, before going 2-0 up after 68 minutes.
Oscar, who scored the winner in Prague on Thursday, met an Ivanovic cross from the right with a back flick which deflected off a defender to go by Moore.
Three minutes later it was 3-0, with Lampard finally finding the target.
Mata made it, dashing down the left and cutting back for Lampard to sidefoot his volley in.
Chelsea sensed the opportunity for more goals and took it when Oscar's inswinging cross to the far post found Terry, who headed in from a narrow angle with Moore floundering.
Luiz needlessly body-checked substitute Jake Reeves as Brentford finished beaten and bruised, with Chelsea advancing to the next round.