Captain Tommy Rowe was the hero with a late winning goal as Posh sank the Championship's bottom side 2-1 in a tense basement battle at London Road.
A controversial Barnsley leveller from substitute Marlon Harewood, with David Perkins seemingly offside in the build-up, proved academic as Rowe beat three men and the keeper with just minutes to go but Ferguson warned that the real challenge is still to come.
"Tommy popped up with a fantastic goal at a great time to earn us an important result," Ferguson said.
"Getting out of the bottom three is a big psychological boost, but my main focus is always on points.
"We're up to 25 after a great run of results at a crucial time in the season but we still need eight more wins to be safe.
"That is a big ask but I've seen a hell of a lot of good things from my players lately.
"They have played terrific football to pick up results recently and then dug really deep today despite being pushed back for much of the second half.
"Barnsley were dominant and probably deserved their equaliser, although you have to question the manner of it. The referee obviously has every right to over-rule a linesman, but what is the point of having assistants at all if that is the case?
"Thankfully we got a second goal and that meant it wasn't such a big issue."