It took 54 minutes before Juan Mata opened the scoring for the Blues against the League One side but goals from Oscar, Frank Lampard and the recalled John Terry then gave the final 4-0 scoreline a flattering look.
Benitez, whose team now travel to Middlesbrough in the fifth round, said: "Credit to them because the first half they were working very hard, but afterwards it was a question of time.
"We knew scoring first could be the difference. They would be more open and we would have more space.
'I'm pleased to score four goals and create chances. I'm really pleased with Oscar and Demba Ba did a great job keeping them busy."
The Spaniard also paid tribute to Lampard after he took his tally of goals for the club to 199.
"The team is doing well and Frank is on fire so he is scoring goals and that is good for him and good for us," he said.
Chelsea have now won three successive matches following last weekend's victory over Wigan and the Europa League defeat of Sparta Prague and Benitez is keen to keep the run going.
"In football you have to win games and for a top side it is even more important because everybody expects you to win every game," he added.
"I have said before that this is a team in transition. I think we have good players and little by little we can manage to improve the understanding between players and everyone is even better and we can continue winning games."