In today's diluted world, with a World Championship every year, people don't understand how much pressure and tension goes with a contest like this.

To get here, you had to qualify. This meant win (or place highly) in a Zonal contest. (Many tournaments - like the U.S. Championship every two or three years - also served as a zonal competition.)

After reaching the Interzonal, well here is where the tension really mounts. Basically, you blow this, and you don't get another whack at it for a very long time ... at least three years, if at all. (Many players made it to the Interzonal stage only once in their life.)

Now to the game ... where did Petrosian go wrong? For a long time it looks like Black is better ... or maybe even winning. Definitely Black's 33rd move (...Qd8) is a blunder. (33...Qe7; looks OK - I checked it on Fritz 8.0. After ten minutes, it gives a slight edge to Black! This might be a bit over-optimistic ... I would say that the position is unclear - possibly even completely balanced.)

This game might have seriously affected the careers of both player. In the tournament, after this game, Olafsson basically collapsed. Petrosian, however, seemed to get better in very game. (Less than two years later, Tigran Petrosian became the World Champion.)