This one is tricky: Black to play has only move that draws. All other are losing.
Defensive resource puzzles
As a puzzle, the diagram 1 is perhaps more suitable for lower rated players (like myself). I didn't resign there but I messed it up. Naturally, the "find the only defensive resource" caption makes it way easier than in real life. Especially if you consider psychological effects, like being frustrated from overlooking a fork.
Please, post here any puzzles with the following theme: The side to move appears to be completely lost, but there exist one (ideally an only one) way how to save the game.
The following example is from my game where I messed it up. (Black to play. Find the best move.)