Posh followed other recent winners at Meadow Lane - Grimsby and Wycombe - in completing the double over Notts and enhancing their own promotion prospects.
But when Peterborough took a 40th minute lead it was their first finishing effort on target and one which completely changed the character of the match and the atmosphere around the stadium.
It was a clear error on the part of Notts defender Brian O'Callaghan which gave Danny Crow a shooting chance for his 12th goal of the season.
There was another blow during the interval when Notts lost debutant Noe Sissoko to an injury, to be replaced by Chris Palmer. Sissoko had impressed and one delightful piece of work down the left-hand side finished with a centre that cried out to be converted but was utterly neglected.
Notts also had a chance earlier in the first half when Peterborough goalkeeper Lee Harrison could do no more than parry a fierce drive by Lewis McMahon, but when the ball fell into the path of Kelvin Wilson he scooped it tamely into the keeper's arms.
Notts were made to pay for these chances when Peterborough doubled their lead just before the hour. There were opportunities to clear their lines but the Notts defenders were hesitant and James Quinn found the net from close range with Notts goalkeeper Kevin Pilkington completely unprotected.
Notts went to pieces for a while only to be revived when Sean St. Ledger handled a scoring attempt and was fortunate not to see a red card. Eugene Dadi, for the second time in his brief Notts career, converted the penalty.
Although Mike Edwards headed against the post in the closing stages Notts never seemed remotely capable of pulling the game round and Peterborough, who finished the stronger, deserved their success.