Chelsea managed to show the gulf in class that wasn't apparant the first time they played Brentford with a 4-0 win, ensuring their progression to the fifth round.
With Arsene Wenger criticised yesterday for choosing to rest his star players, Rafa Benitez didn't make the same mistake, putting out a strong team.
But the first half was a frustrating one for the Premier League side, with Brentford proving every bit as resilient as they were in the first tie, although Chelsea could have gone ahead through Frank Lampard missed two good chances to go ahead, and Brazilian Oscar managed to clip the wrong side of the post half midway through the half.
The second half saw Chelsea step up a gear and turn on the style. Their first goal however was route 1 stuff, with a long ball from Cech headed down by Ba for Mata to latch on to, and drill home from the edge off the area.
Oscar then showed some typical Brazilian flair when he cheekily flicked home a cross from Ivanovic.
The flood gates had well and truly opened for Brentford now, and Frank Lampard finished from close range from Mata's low cross to score his 199th goal for Chelsea, and become their leading scorer in the FA cup with 26 goals.
Chelsea's other main man John Terry was back in the side and capped his return with a goal, getting his head on the end of Oscar's cross to make it 4-0 and put a sharp end to Brentford's giant slaying ambitions. Chelsea will now have to play Middlesbrough away in the fifth round.
Manchester City also ensured there would be no upset at the Etihad as they put championship side Leeds to the sword.
They managed to do it much quicker than Chelsea had, with Yaya Toure putting them ahead with only five minutes gone, after clever play on the edge of the box allowed the space for Toure to run into and take the ball past Jamie Ashdown and finish coolly.
City were given a penalty ten minutes later when Ton Lees brought down Sergio Aguero in the six yard box, the Argentine then putting the ball on the spot himself, before sticking it in the top left hand corner.
The rest of the first half proved fruitless as City relaxed into their own tempo and Leeds struggled to make a mark on the match, Yaya Toure producing a fine chance with a volley from outside the box, which Jamie Ashdown was able to save.
Less than ten minutes into the second half the game was over, with Aguero getting into the box down the byline, and playing to the onrushing Tevez, who fumbled the ball over the line to put the game beyond doubt.
With the game effectively won, Mancini used the rest of the half to give returning pair Jack Rodwell and Maicon a run out, both having been on the long term injury list for some time.
Aguero finished off an efficient display with less than twenty minutes remaining, finding himself in space to slot past Ashdown and see the ball go in off the the post. City cruised to the final whistle safe in the knowledge they had put on a good display for their fans.