A last-minute spot-kick earned Burnley all three points as the Posh Under 18s suffered their first defeat in four.
The Peterborough United Under 18s were undone by a penalty kick in stoppage time as Burnley left the idverde Training Ground with all three points on Saturday morning, just as it looked like Joe Davies had earned Jimmy Unwin's men a deserved point.
After a quiet start, it was Posh who created the better opportunities before the break, George Holley slicing wide after good work from Davies and Joel Odei-Larbi just unable to convert at the back post after Noah Freeman's shot into the ground veered into his path.
Eddie Fox headed over on the stroke of half-time after a lovely cross from Freeman but moments after the re-start, Posh keeper Jake West was called into action, keeping out a low drive from Archie O'Brien.
West kept out Mursalov twice, first with his legs and then by pushing a shot around the post. He made a double stop on 59 minutes keeping out two Burnley players in quick succession.
Substitute McWilliams-Marcano saw a curling shot pushed away by the keeper as Posh tried to find the breakthrough.
On 72 minutes, Burnley opened the scoring as a corner kick was met by substitute TIOFFO who headed back across goal and into the corner,
The Posh left-back, Trialist A saw an effort trickle just past the post on 89 minutes after a forceful run but moments later, he played a key part in the equaliser, cushioning a cross back into the path of DAVIES who made no mistake from close-range.
However, the visitors went straight down the other end and won a penalty with TIOFFO coolly sending West the wrong way from 12-yards.
Posh: West, Freeman, Trialist A, Holley, Claxton (sub Gilbert 65min) , Mendonca, Davies, Fox, Trialist B (sub Shofowoke 65min), Beech (sub Sykut 79min), Odei-Larbi (sub McWilliams-Marcano 46min).