Third division strugglers Leyton Orient ended their goal drought as they struck three times in the first 31 minutes to send second division Peterborough crashing out of the LDV Vans Trophy.
All the goals came in the opening 32 minutes of a pulsating first half.
But Orient took the lead when on-loan signing Izzy Iriekpen, who had signed from West Ham just hours before the game, headed home from close in.
Donny Barnard scored his first ever goal for the club on 19 minutes when he headed home a John Martin cross but Peterborough striker Andy Clarke cut the deficit shortly afterwards.
Orient stretched their advantage when defender Matt Lockwood curled in a shot from the right but Peterborough's response was instant as Clarke grabbed his second goal on 32 minutes to complete the whirlwind goal rush