1.D5 is a desperate-looking move that manages to bring White through a lost quadrant game to win the large game.

Quick glances at the top and right quadrants will reveal that they are White's; but the left and bottom quadrants belong to Black and cannot be taken from him. And Black appears to have a strong advantage in the large game, making an overall 3-2 Black win seem very likely.

However 1.D5 enables White to buy the time that he needs. Black must play 2.C4 to keep the lower quadrant; White can threaten it again with 3.D4, forcing 4.C3. Now White plays 5.E4 and he's navigated his way through the lost subgame to connect up with his stones at F4 and F3!

(You may want to verify for yourself that no matter what Black does, White will win the large game and moreover hold on to his two won quadrants.)

This puzzle was amended slightly to correct a problem noticed by Paul van Wamelen.