The son of United manager Sir Alex steered Posh to their third promotion in four seasons with a 3-0 victory over Huddersfield at Old Trafford after late goals from Tommy Rowe, Craig Mackail-Smith and skipper Grant McCann.
Ferguson senior was not present to witness his son's victory but shortly after the game the London Road boss spoke to his father, whose United side were outclassed in losing 3-1 to Barcelona at Wembley on Saturday.
Peterborough manager Ferguson - a former United player - said: "It's the best day of my career, both as a player and as a manager.
"After last night, with my dad losing, I wanted to get this win to put a smile back on his face.
"I've just spoken to him, and I've certainly done that, so I'm pleased and he's delighted.
"It was obviously a big weekend for the family and there were always going to be three different possibilities.
"The way it's turned out, at least one of us has got a win."
Ferguson, 39, jokingly claimed his father was a "jinx" after his side had lost a number of games that the United manager had attended.
"He came to the play-off semi-final first leg at MK Dons and we got beaten," said Ferguson, whose side made an immediate return to the second tier.
"He's not seen me win for a while, but he stayed away from the second leg and we won, so we decided he would stay away from this one."
The result further restored Ferguson's reputation after he was sacked by Preston North End in December after leaving London Road in November 2009 before returning for a second spell earlier this year.
Since Ferguson's sacking at Deepdale, Preston went down and Peterborough have gone up.
"I'm not a bitter man," said Ferguson.
"You have ups and downs in your life and you have to deal with that.
"I've done that in my own way and I definitely learned more at Preston than I have in my other years as a manager.
"I could have gone into my shell and not come back for a while, but I was determined to succeed as a manager.
"I'm lucky. I've won three promotions and some managers don't win any."
Peterborough were worthy victors, although their late flurry of goals came after Huddersfield had enjoyed a period of sustained pressure.
"The thing that won us the game was that we didn't concede," said Ferguson, who revealed Mackail-Smith's 35th goal of the season is almost certain to be his last.
Several clubs are courting the Scotland striker, who caused the Huddersfield defence untold problems all afternoon. "You would have to say the odds are stacked with him probably leaving," said Ferguson.
"We would have to get the right money for him but everyone would wish him all the best.
"He's earned the chance to go and play at a higher level.
"We need other players and we have to try and establish ourselves in the Championship now."
At the final whistle Ferguson warmly embraced Huddersfield counterpart Lee Clark, who could not his disappointment after the game.
It was the second successive season that Clark's men had failed in the play-offs and another massive setback to the ambitious Yorkshire outfit.
Huddersfield had not lost in 27 previous league and play-off games, and Clark, 38, said: "We knew this was a one-off game but the players don't have to feel ashamed about anything that has happened this season. The scoreline is harsh but take nothing away from Peterborough.
"The one consolation is that a good man in Darren Ferguson and some good people at Peterborough have gone up.
"They withstood what we threw at them and then hit us with a treble. They got the touch in for the free-kick for the first, the second was deflected and then the lads lost a bit of shape.
"It wasn't to be but they didn't deserve to lose 3-0. I'm hurting and I need to get away and spend some quality time with my wife and three children.
"I need to get my batteries recharged because I'm physically and mentally drained and then come back and see where we go.
"I know what it takes to bounce back because I've done it before.
"We've had an unbelievable season but we haven't achieved our goal."
Huddersfield: Bennett, Hunt, Peter Clarke, Kay, Naysmith, Roberts, Kilbane, Peltier, Arfield (Lee 81), Ward (Cadamarteri 79), Afobe (Rhodes 81). Subs Not Used: Colgan, McCombe, Gudjonsson, Novak.
Peterborough: Jones, Little, Bennett, Zakuani, Basey (Lee 64), Wesolowski, McCann, Rowe (Whelpdale 84), Boyd, Tomlin (Ball 90), Mackail-Smith. Subs Not Used: Richardson, Langmead, Mendez-Laing, Newell.