Posh manager Darren Ferguson leapt to the defence of goalkeeper Joe Lewis who pulled off a superb penalty save in time added on to keep his side in the automatic promotion hunt.
Lewis, who has come in for some flak from supporters after recent blunders, kept out Luke Summerfield's spot-kick after Lee Frecklington had tripped Stephane Zubar in the third minute of injury time.
Posh had hit back after falling behind to Carl Fletcher's 38th-minute opener with second-half goals from Ryan Bennett and Craig Mackail-Smith, who struck his 30th of the season.
Posh manager Darren Ferguson hit back at Lewis' critics, saying: "Joe was absolutely outstanding for the whole game.
"The Plymouth goal is absolutely nothing to do with him. He has then made a stunning save just after we got in front before also keeping the penalty out.
"But I suppose in many peoples' eyes he will have been rubbish as usual, so there we go."