The one-time Arsenal and Nottingham Forest shot-stopper was in commanding form for the bottom of the table side and helped them frustrate Posh to claim their first point since the opening day of the season.
Chasing a third successive home win, Posh were twice denied by the woodwork in the first half, Peter Gain seeing a low cross shot come off an upright after he cleverly jinked past two opponents and, despite beating Marriott, teenager Jamie Day suffered the same fate with a header from Adam Newton's swirling centre.
Although Posh generally managed to keep a tight rein on London Road old boy Leon Constantine, a Torquay £75,000 club record capture last season, 19-year-old Liam Coleman found space on the edge of the area and sent in a rising shot that Mark Tyler saved impressively diving to his left.
Posh boss Mark Wright increased pressure after the break sending on additional strikers Richard Logan and Trevor Benjamin to link up with Northern Ireland international James Quinn, former Boston man Logan coming close to making an immediate impact with a header that Marriott did well to hold.
But Logan wasted a glorious opening set up by David Farrell's cross when placing a header wide of a yawning target from just six yards.
Benjamin, disappointing so far, produced a spectacular overhead kick that was straight at Marriott and Torquay rode their luck to the very end with Matt Hockley scrambling Logan's glancing header off the line to keep a clean sheet.
Ironically, Constantine might have had the last word, breaking away as the game went into five minutes of added time to force Tyler into a spectacular flying save.