The Hi Hi secured the South Division title with a win over second bottom Pumpherston.
Top scorer Joe Murray hit the underside of the bar with an overhead kick in the first minute and it was his excellent cross from the right touchline which provided skipper Chris Gray with the opportunity to pick his spot for the opening goal six minutes in.
Haddington replaced Mark Smith with 17-year-old Kyle Mitchell, on loan from Cowdenbeath, at half-time, and he was to play a pivotal role.
Pumpherston equalised with 20 minutes remaining when, from a contentious free-kick, Darryll Butler’s back header found its way into the net and it looked like the title celebrations would be curtailed seven minutes later when home defender Chris Gordon guided the ball past his own keeper Derek Polowyj following a communication mix-up.
Mitchell, however, levelled a minute later with a close-range finish, and Gray put Haddington back in front from the penalty spot with eight minutes left after Murray was fouled. Almost five minutes into injury time Mitchell carried the ball deep into the box, his shot was blocked but the ball fell to Gray who completed his hat-trick to kick-off the party.
Haddington: Polowyj, McPartlin, Noble, Gordon, Motion, Fairnie, Smith, (Mitchell 46), Ponton, Wright, (Sinclair 82), Murray, (Slight 89), Gray. Unused subs: Szemis, Gallagher.
Pumpherston: Hunter, Campbell, Spooner, D McKenzie, Butler, Purvis, Slessor, McLaughlan, Lawrie, Douglas, Rae. Subs: Grieve, Nimmo, Martin, Forret, McGuigan.