Chastened by a 10-point defeat in Down 12 months ago, London gained revenge with a fine display at Ballycran on Saturday.
Playing with a strong breeze in the first half, they started well but were caught napping when a defensive mistake let Chris Egan scoop to the London net.
Their response was impressive, restricting Down to a single point in the last 20 minutes of the half while keeping the scoreboard ticking over themselves.
Kevin O'Loughlin's goal came within a minute of the Down effort, and the same player's frees punished Down's indiscretions. Ger Mahon struck a brace of long-range points and London turned around nine points to the good.
With London leading by 10, Egan again punished a defensive error and Down chipped away at the lead until the gap was just three.
However, an incisive London move freed Shane O'Donnell and from 10 metres he blasted to the net to finish off the game.