Siriki Dembele grabbed Peterborough's winner to haul them out of the Championship bottom three with victory away to fellow strugglers Hull City.
Dembele's calm finish, clipped over Matt Ingram 18 minutes from time, earned Posh their first away points of the season as they leapfrogged their hosts in the table.
Jack Taylor's long-range effort put Peterborough ahead just before the break, only for Josh Magennis to head an immediate equaliser for the Tigers.
But a dreadful second-half penalty miss by Magennis enabled Dembele - who also scored the decisive goal in his side's 2-1 triumph at Hull last season - to settle things again.