Boyd - extending a club record with his 126th consecutive appearance - opened his account on 25 minutes with a delightful shot from 18 yards.
He sealed the win from the penalty spot 12 minutes from time.
Ferguson said: "That's 126 games now and he is looking tired - but how can you leave him out, he's special? Yet this was a team performance - we could have won by six."
Posh grabbed their second on half-time when Craig Mackail-Smith pounced on a slip from defender Jordan Spence.
Iron boss Nigel Adkins said: "The turning point was that goal, it was a costly mistake by Jordan."
This article has 0 comments