Craig Mackail-Smith was on hand to head a 61st-minute equaliser as Posh came from behind to share the spoils in a 1-1 draw at London Road.
Mackail-Smith rose above Owls defender Tommy Spurr to convert a splendid left-wing cross from Tom Williams.
It cancelled out a first Wednesday goal for James O'Connor which had given the visitors the advantage in the 21st minute, but was not enough to full satisfy Posh boss Ferguson.
He said: "It is a game I felt we deserved to win and one that we should have won.It was disappointing to concede in the manner we did because we had spoken about their lad coming forward from midfield.
"We know we have to be more ruthless in both boxes and that is something we will ensure happens.
"I can't have too many complaints about the performances, but getting results is the thing that matters."
Posh had the better of the early exchanges before Wednesday hit the front in their first attack of any real note.
Aaron Mclean lobbed an excellent chance on to the roof of the net with Owls stopper Lee Grant stranded after springing the visitors' offside trap before wideman Tommy Rowe saw an effort from an acute angle hacked off the line by Spurr.
But it was the Owls who broke the deadlock when former Burnley man O'Connor scampered forward into the box to be picked out by a Marcus Tudgay cross and given plenty of time to steer a header past Joe Lewis in the Posh goal.
Mackail-Smith drilled a fine chance wide as Posh burst out of the blocks in the second period but he made amends just after the hour when hauling the hosts level.
That goal gave Ferguson's men a noticeable lift. Substitute Shaun Batt and George Boyd both saw efforts blocked as they upped the ante, while Lewis was called on to keep out a Tudgay drive after a clever free-kick routine.
Wednesday boss Brian Laws said: "It was never going to be easy going to Peterborough for their first home game back in the Championship.
"They are used to winning, the crowd really get behind them and they have some very good players that we marshalled well, but I must admit we are a little bit disappointed not to have picked up all three points.
"But this is the sort of match we might well have lost last season, so we are definitely going in the right direction."