The Blackpool boss watched in disbelief as his side put up no fight at all against Barry Fry's doomed side.
Pool midfielder Keith Southern saw a penalty saved just after the half hour after Keigan Parker was brought down by Mark Arber.
And Calum Willock blasted Posh ahead three minutes before half time when the entire home defence went awol.
Hendry raged: "That was a disgrace. I'm not going to make any excuses for why we played like that and I am not going to defend my players. I have stuck up for them in the past but this was a terrible performance.
"I feel sorry for the fans who have paid to watch and I am not going to accept the blame. The players can accept it.
"The preparation was no different than for any other game and I cannot explain what went on out there.
"At no stage this season have I taken my eye off the pack behind us and this result means we have a fight on our hands to make sure we don't get dragged into a relegation dog fight."
Peterborough manager Barry Fry, who will retire in the summer after 31 years in management, said: "My players deserved that and I am proud of them all.
"I am disappointed to only come away with a 1-0 win. The lads have deserved a victory for the last few games. They have worked very hard and they have been playing very well.
"We hit the woodwork twice and it says a lot that the Blackpool keeper was named man-of-the-match.
"There were some very good performances. Our goalkeeper played well, he made some important saves, and the two boys upfront caused lots of problems.
"But the whole team put in a performance that shows we are not going to wave the white flag.
"We may well be all but relegated but we are not going to go without a bit of a fight."