The recent striking recruit from Macclesfield Town was handed a first start and responded with his first two goals for the club.
That was enough to sink struggling Burnley 2-1 and leave Ferguson all smiles, but he was anxious to stress it was not a one-man show.
Ferguson said: "Emile is a great lad who wants to be a top player. He turned down other Championship clubs, who would probably have been offering more money, to come here.
"We knew we were buying someone with a lot of pace and he showed that he can finish as well.
"People think we are all about attacking so I feel it is only right to praise the back four and goalkeeper as well. They were outstanding and this is easily our best result of the season so far. We dug in and saw it out."
Sinclair needed only three minutes to repay his manager's faith with the opening goal, collecting a Lee Tomlin pass and rifling past Burnley keeper Brian Jensen.
Only a last-ditch goal-line clearance from defender Ben Mee prevented him doubling his lead soon after and Ryan Tunnicliffe headed another excellent Posh chance into the side netting.
Burnley then lost Jensen to a groin injury before coming alive in the attacking third. Posh keeper Paul Jones denied Charlie Austin, Jay Rodriguez, Chris McCann and David Edgar during a frenetic couple of minutes.
But it was the hosts who struck again when Sinclair caught full-back Kieran Trippier dithering, held off a couple of challenges and coolly slotted past substitute keeper Lee Grant.
Any thoughts of a Posh stroll were dispelled when Keith Treacy spectacularly halved Burnley's arrears in the last minute of the first half with a 25-yard screamer, but the visitors were unable to find another way through.
And the same applied to Posh as Sinclair could not convert a couple of decent chances to complete a hat-trick - firing one into the arms of Grant before blasting another opening wide.
But his brace proved to be enough to sink a Burnley side whose boss Eddie Howe is bracing himself for plenty of flak after just one win so far this season.
Howe said: "Managers are judged on results and ours are not very good at the moment.
"I'm accountable for that and am prepared for whatever criticism comes my way, but we really need the fans to stick with us and back the players.
"I really thought we should have won this game. Our passing and movement was excellent but we paid the price for two lapses of concentration which allowed Peterborough to score.
"Their goalkeeper made a number of good saves but we should have done better on several occasions."