The hard part at this End was to make a good exchanges here and use a bad White's pawn structure, by creation a position, with zugzwang, to intrude a Black King into the Pawn's grabbing and Won position...
One lost tempo, and the Draws chances may grow!
On that position it was just right enough Tempos, to create a Zugzwang for White!
33. a3 a4. Zugzwang!