The Blues struggled to break the Bees down early on but took the lead just after the break through Juan Mata.
Look back at how Chelsea booked a fifth-round trip to Middlesbrough with Sports Mole's minute-by-minute commentary below.
BRENTFORD: Moore, Logan, Dean, Craig, Bidwell, Douglas, Forshaw, Diagouraga, Adeyemi, Donaldson, Trotta
"It's one of the games you dream of and is what the FA Cup is all about. All the players are relishing the chance."
"I think we didn't do as well as we were expecting [in the first game], hopefully we will change that today. I was thinking about changes and John Terry has been training so he is ready. The pitch has to make a bid difference today and we will be ready."