Football League chairman Lord Mawhinney and campaigners from Peterborough's 1970 promotion squad turned out at London Road for the opening of a Noel Cantwell Suite to honour the memory of former Posh manager and Manchester United, West Ham and Ireland skipper who died last year.
They all saw Steve Bleasdale's side gain the lion share of first half possession and find plenty of width through Adam Newton and David Farrell on a muddy surface. But few openings were created and defender Mark Arber went closest, jumping well to get in a strong header that Boston's Michels Kuipers clutched to safety following a corner.
Despite a couple of neat touches from Peterborough-born Julian Joachim, Boston posed little threat and up to the break home goalkeeper Mark Tyler had not been troubled. As the one-way traffic continued, Posh top scorer Danny Crow wasted a gilt-edged chance screwing his shot well wide after a fine delivery from Farrell.
Joachim almost caught Posh out with a snap-shot that brought a superb one-handed save from Tyler and, as the Pilgrims maintained the momentum, substitute Clarke, who had replaced injured ex-Posh midfielder Simon Rusk just after the turn-around, made the decisive strike. The Sunderland-born 23-year-old was left unmarked as Posh struggled to clear a corner and seized his chance to volley past Tyler from 10 yards.
Posh flung everything into attack in the closing minutes and, despite the efforts of Farrell and substitute Lloyd Opara, Boston's experienced pairing of Austin McCann and Paul Ellender never lost their grip at the heart of defence.