A pawn on the fourth rank wins if the defending king is cut off by two files. The attacking king and pawn advance together while the rook keeps the enemy king at bay.
Same pawn, same rank as in the frontal-defence lesson, but the black king is on g7 and the white rook on f1 cuts it off by two files. That extra file turns the draw into a win: the black king is too far away to interfere with the pawn's advance.