I was going to comment on the recent Carrelli-Pawlowski game from the Kenilworth CC summer tournament, but I don't have the score in front of me anywhere so that will have to wait. The short version is that Don managed to sac two queens (!) in a brilliant win. Given that we're proud of Don when he laces his shoes correctly, this was a stunner. But back to the position from Portisch-Petrosian from earlier, after 47. Kxf3:
To answer the last question first, if the pawn were on the a-file, this is a dead draw, simply because Black's rook is placed excellently behind the passed pawn. Black's rook can check White's king endlessly from this position because it will have nowhere to hide except in front of the pawn, which impedes its progress. If the opposite were true and White's rook were behind the pawn, the position becomes winning for White because Black's rook is forced to be entirely passive, guarding the a-file while White's king runs rampant. See for example Alekhine-Capablanca 34th game WC match (1927) 1-0. Alternatively with the Black rook behi
nd the pawn see: Federowicz-Yermolinsky USA Ch (1997) 1/2-1/2.
So what happens on the b-file? It turns out to be quite tricky. In fact, in this case, former world champion Petrosian lost the game, even though he had an overnight adjournment with helper monkeys to solve the puzzle. First let's see what has since been determined to be Black's best approach to a draw (according to Kantorovich):
47....Kf6! 48. Ke3 Ke6 49. b5 b5 Ke5 50. b6 Ke6
It seems that White has made all the progress and Black
is merely marking time. However, after: 51. Kd4 Rb1 52. Rb8 Kd6 53. b7
It turns out the Black is completely safe with the paradoxical 53...Ke7!
With the White rook on b8, this position is functionally identical to one in which the pawn is on the a-file, since Black's rook can check the White king at will, which has no shelter and no way to advance the pawn. As long as Black's king stays away from cheap tricks (54...Ke6?? 55. Re8+ wins), there is no progress to be made. Likewise, had White advanced his pawns earlier in this variation it makes no difference, all Black has to do is keep White's king away from his pawns.
Petrosian did not find this defense, but it is psychologically difficult to defend so passively so perhaps this is no surprise. What he did find was an active plan, one that could have succeeded:
47....Kh6 ?! (Kasparov) ! (Emms)......!? (Mangion)
Until the above defense was found Black's idea seemed the most compelling - he intends to advance his pawns and create a weakness in White's position that can provide counterplay and shelter for his king. There is a long series of analyses of the strength or weakness of this move in On My Great Predecessors Vol. 4 which I'll leave to the hard-core. I like Black's idea because I think it would succeed against most opponents and is easiest to understand as well.
48. Ke3 f6 49. Rb6 Kg7 50. Rb7+ Kh6 51. Rb8 g5 52. b5 gxh4 53. gxh4 Kg6!
While White has temporized Black has made real progress toward his goal - White's kingside is now weak and Black threatens to enter on f5-g4, then taking the h-pawn.
54. b6 Kf5 55. Kd4 (hoping to queen faster than Black) Rxf2?
But here Black deviates from his own plan. It turns out that 55.....Kg4! 56. Rg8+ Kxh4 57. Kc5 Rc2+! can draw, as Black pushes White's kin
g in front of his own pawn so that ...Rxf2 comes with a gain of tempo, then the rook is sacrificed for the b-pawn, after which Black is just fast enough with his pawns to force White to sacrifice his rook back for the draw (it takes the computer quite awhile to spot this).
56. Ra8! White uses the tempo he has been gifted to maneuver his rook to where it can both check the Black king and get behind his passed pawn.
56....Rb2 57. Kc5 Rc2+ 58. Kd4 Rb2 59. Ra5+ Ke6 60. Kc5 Rc2+ (it turns out that 61...f5 can lead to a drawing sequence for reasons I can barely understand. Checkout Kasparov's analysis for details) 61. Kb5 Kd6
White has hit on a winning plan - under the cover of his rook, the White king can force the advance of the b-pawn, the rest is easy:
62. Ka6 Kc6 63. Ra1 Rc4 64. b7 Rb4 68. Rc1+ Kd7 69. Rc8 1-0
'A famous endgame, which appeared in chess publications right around the world' - Kasparov