BLACK TO MOVE

Find the only winning move for Black.

Black to move and win

From the Chesstempo rapid game Paldrick - Nanomaster, I had black pieces.

BREAKTHROUGH

On the platform Chess Mail, where the chess engines are prohibited, I had white pieces against Telemaque in correspondence chess. I thought I had a winning position but could not break through. The opposite-coloured bishops were on the board, and my opponent had built a fortress. 

Making the move 1 Ra5-a1, I gave up my hopes of breaking through on the queenside by making some sacrifices.

I was ready to offer a draw if my opponent plays 1...Kf5-e6.

Suddenly, my opponent made a grave mistake 1...Kf5-g4??

It is White to move and win. 

And do not say you will win if you make the second-best move in that position. Whatever the chess engines are telling you.

White to move and win

In the present post, the Apronus chess software was used.