Lee Tomlin was the two-goal hero as Posh cruised into the second round, while Gabriel Zakuani, Tyrone Barnett and Tommy Rowe were also on target in a landslide victory.
Ferguson said: "Our work ethic was very good in the first half, but some of our simple passing was sloppy.
"We couldn't have made a worse start to the second half, conceding an equaliser, but our reaction after that was excellent.
"Colchester tried to get in our faces, but we played very well and, in the end, it could have been more than five.
"Our attacking play was excellent and we looked fit, quick and powerful. In the end they couldn't live with us.
"On Saturday we weren't ruthless enough, despite playing at such a high tempo, but here there's no question that we were.
"We watched Colchester on Saturday. They've got some very good players and they try to play a similar way to us, passing the ball forward from the back.
"On this performance, my lads were very good."