The first position in the series on Petrosian's Exchange Sacrifice, one of the most famous positional sacrifices of all time, is shown in the diagram.
[FEN "3rq1k1/4rppp/2n3b1/pp2P3/2pP1QB1/P1P1R3/1B4PP/4R1K1 b - - 0 25"]
In a wonderful example of verbal analysis, Petrosian wrote:
The situation is very tense and complicated, materially balanced. So-called dynamic balance exists, with even chances for both sides in attack and defense. White has a strong Pawn center which would smash Black's position if put into motion. On the other hand, it is not easy to advance White's central Pawns; no use of e5-e6 and no sense of d4-d5. Therefore I was satisified with this position until I reached it. But when it stood on the board I realized that Black's position is rather difficult. You may ask, why? Because Black's pieces are posted passively, limited strictly to defense. White can prepare the advance of his d-Pawn to d6, throwing Black's pieces back and achieving a winning position. On the other hand, White has the possibility of advancing his h-Pawn: h2-h4, threatening h4-h5-h6. If Black reacts h7-h5 or h7-h6, he creates weaknesses on his Kingside giving White a good attacking opportunity; the Bishop will go to c1 and join the main forces.
I realized that by moving my Knight to d5 I would change the situation completely so as to make it very favorable instead of difficult. White's Pawns would be blockaded; his Bishop on b2 would be very poor; after an eventual b5-b4 Black could obtain a passed, very powerful Pawn supported by Nd5 and Bg6. However, it is very difficult to bring the Knight to d5. This could be done via b6, c7, or e7, but a Knight maneuver to b6 or c7 would take a lot of time; White plays Bg4-f3 and d4-d5, obtaining a winning position. Of course the idea of moving the Knight to e7 is highly welcome, but how to do it? First I should go away with the Rook, but where?
I spent a good deal of time thinking over this position, and when I found the right move I felt kind of amused. The move was so simple that there was no doubt about its correctness. I overcame the psychological barrier and put my Rook under the fire of White's Bishop. (Petrosian's Legacy p.68)
Petrosian played 25...Re6. In the tournament book, considered one of the best chess books ever written, Bronstein summarized the positional ideas this way:
Black must block the White Pawns, and Petrosian immediately offers the exchange in order to free his e7 for the transfer of his Knight to d5. True, Black gets serious compensation: his Knight on d5 will be exceptionally strong, as will his Bishop, which will lack a light square opponent. Notice that now or on his last move White could have started a direct Kingside attack by h2-h4-h5 and Re3-g3, getting good winning chances; but he counts on winning in another way.
Reshevsky delayed the capture for one move with 26.a4 Ne7, but finally played 27.Bxe6 fxe6, and was unable to win. To play through the complete game see...
Samuel Reshevsky vs Tigran Vartanovich Petrosian, Zurich 1953