An early Mauro Formica goal put the visitors in front at London Road, and Jordan Rhodes then scored a hat-trick before lee Tomlin got Posh on the board late on.
The result left Ferguson's side bottom of the Championship on goal difference, but he said: "I really enjoyed watching some of our football.
"We had started the game brightly so to concede such an early goal was a big blow, but I give credit to my players for not going under against a team with a hell of a lot of decent players.
"A lot of people might have thought Blackburn would go on to get five or six but we stuck to our task and kept looking for the ball.
"We got control of the midfield, but matches are won in both boxes. We now have away games at Ipswich and Charlton which will be key in our season."