The only way I got this was by grinding out the calculations--I had absolutely zero intuition of what the right moves would be. Quite literally I wrote out the calculations a post-it note. I can't believe people would find this stuff (or any Sunday puzzle) OTB.

It's amazing that Fischer had the idea of inflitrating White's position around move 21, where the liquidation of material begins to take place.

I'd say those knights and rooks are the most pathetic things i've ever seen in a closed pawn position..

Material: even. White has the bad B and his entire position is constricted.

SPOILER WARNING: This is the mother of this week's second-best moves!!! I not giving myself any credit, it is probably not worth reading, and I really should learn when to give up. It was interesting, though...

Candidates (46...): Rxb1

[I dismissed Fischer's 46...Ra2 as completely ineffective.]

The move 46.Rxb1 seizes the opposition and permits the White K to penetrate further to intensify the pressure on Pc3.

46...Rxb1 47.Kxb1 Kb3 48.Be1

Candidates (48...): Bxb4, Nxc3, Na3, g5, h6

Let's sample the interesting sacrifice Bxb4 first, because it is most forcing, and because K-side P play can be sought at any time. Note that any line with an uncompensated exchange of Black B for White N is a win, because the White B is so bad.

48...Bxb4 49.cxb4 c3 50.Kc1

No immediate progress appears possible, but Black's position on move 48... can be improved, because White is so passive. White's Ne1 must stay put as long as Black's N threatens Pc3 and cannot stray far, and his B and K can at most shuttle Be1-d2-e1 and Kc1-b1-c1.

Black therefore tours his Nb5 with Nb5-c7-a8-b6-a4 and an intermediate b5. Because Black can burn tempi with his B, he can achieve an equivalent position (outside irrelevant K-side P moves), Black to move, with the Black Pb6 at b5 and the Black Na4, and with the White Kc1 and Be1 or with the White Kb1 and Bd2.

Start the move count when the position is achieved with Black to move:

1...Bxb4 2.cxb4 c3

Case 1: White pieces are Kb1 and Bd2. All pieces must be exchanged at c3 (else 3...c2), leaving White with a won K+P endgame.

Case 2: White pieces are Kc1 and Be1. The lines in Case 1 pertain, so only one viable defense remains.

3.Nf2 Nb2

All defenses fail.

4.Nd1 Nd3+ and 5...c2+ 6...c1=Q

4.Kb1 Nd3 5.Nxd3 dxe3 and after the exchange on d2 of 2Ps for B, Kxb4 and the game is won.

4.Bxc3 Kxc3 and White has a won K+N+P endgame.

That leaves (c) 50. Bd2, in which case Black resorts to slow strangulation. The winning plan is to shift operations to the kingside by 50...g5! If White does not take the pawn, Black can continue with ...g4, followed by ...h5 and ...h4. If White does play 51. fxg5, then Bxg5 followed by ...h5 and ...h4. I figure, one of the following has to happen:

(1) The Black bishop gets to h4, when ...Ne1 followed by ...Nf3 puts White in zugzwang.

(2) The Black pawn on g3 becomes isolated or backward. In this case, the bishop wins the pawn and again gets to the h4-e1 diagonal.

(3) The White pawns get to h3 and g4, when ...Bh4! forces the promotion of one of these pawns.

Is there a defense for White?

Excellent endgame by Fischer, who made it look easy. The following article shows how a difficult the endgame really was:

Recurring theme is an understatement.