Seventh-placed Swindon are the only side who can deny Ferguson's side a play-off place, but the Robins must claw back a four-point deficit in the remaining two games of the season.
Britt Assombalonga's two second-half penalties clinched victory after Conor Washington's first-half strike had given the hosts the lead, and Michael Bostwick added a fourth in injury time.
Ferguson rotated some of his squad for the game and said: "It was a convincing win, although I was a little disappointed that it was only 1-0 at half-time.
"But I thought we looked convincing, I thought we looked confident and the ones who came into the team did well. So I was pleased.
"It was a confidence performance. After the defeat against Bradford we could have been edgy, especially after Swindon scored in the last minute against Coventry.
"As a manager I've got a good trust in all my players so I was always going to mix the pack.
"My squad is decent and are much of a muchness. There are no superstars here and they are a good bunch.
"We spoke about our aspirations to finish sixth and get in the play-offs and are fully aware that we will be at home first.
"So we need to take this momentum and confidence into the first leg.
"Without getting ahead of ourselves, we've got to get there first.
"That's four convincing victories at home now, but I'm disappointed that we didn't get the clean sheet as well."