With key front men injured, Barnet boss Paul Fairclough opted to pack midfield and his patched up side took the game by the scruff of the neck and were good value for their ninth minute lead when veteran Andy Hessenthaler, the oldest player on the pitch at 40, fired past Mark Tyler from six yards.
Chasing a first away win since August, Barnet could have added to their tally with Tyler having to deny Liam Hatch before defender Simon Clist went forward and sent a header looping on to the top of the net.
It was more than half an hour before Ross Flitney was brought into serious action and even then the flag was going up for offside as the Barnet keeper went full stretch to save from Peter Gain.
One good home spell just before the break saw Sean St. Ledger's shot blocked following a corner and then Danny Crow fired straight at Flitney.
Crow made no mistake levelling eight minutes into the second half, the former Norwich youngster running onto an inch perfect pass from Gain before calmly lifting the ball over Flitney for his 13th goal of the season.
Incredibly, Posh found themselves trailing again on 70 minutes, Dean Sinclair cleverly back heeling into the path of Barry Fuller who gave Tyler no chance.
However Barnet's lead lasted only five minutes when substitute Richard Logan fired home following a dangerous corner from Ryan Semple.
Even then, Barnet might have snatched victory. As the game went into added time, Hatch stormed forward only to waste a determined run by shooting hurriedly and high over the bar.