An interzonal chess tournament was held in Portorož, SR Slovenia, SFR Yugoslavia, in August and September 1958.

[2] In the final round Fischer had black against Gligoric; while Bronstein, Olafsson, Szabo and Pachman had relatively weaker opponents.

The tournament was notable in that the two top finishers, Tal and Keres, scored heavily against the bottom of the field.

Due to Tal's less impressive results against the very top players, including his three losses to Keres in the Candidates, Botvinnik was the favourite.

He believed that the move would throw Botvinnik off and that it could only be exploited by opening the game for Tal's bishops.