Snatching Defeat from the Jaws of Victory

Here is a favorite position from one of my early USCF tournament games. I had Black against an expert-rated player, and I was in trouble: White had trapped my queen earlier in the game, and my position was in tatters. My pinned bishop on g7 was looking quite useless, especially in light of Nimzovich's famous quote: "The defensive power of a pinned piece is only imaginary."

I envisioned my swift demise, so I attacked desperately. My last move ...Rb4+ was met with Kb1-c1 (see diagram). Too bad for me that I did not recognize White's move as the blunder it was! [Kb1-a1 was better.] I missed the best continuation and subsequently lost the game. ["The winner of the game is the player who makes the next-to-last mistake." -- Tartakover] 

The position makes for a nice puzzle. Enjoy!

[Note: For more fun and quotes, check out the move-by-move commentary when finished.]