Why Tal played 1.Nf3 is beyond me, Keres hardly ever played the Sicilian, Maybe Tal was trying to play a Sicilian via 1.Nf3,c5 2.e4. After 1.e4 Keres might have played 1...e5 a closed Ruy lopez would most likely have been played.

It may not be a lost position, but he certainly gives White a good position out of the opening.

Keres writes, "This game was played in the last tour, five rounds before the end of the tournament. At that moment, Tal was leading by a margin of 2.5 points over me. I had therefore to play for a win at all costs in order to retain even theoretical chances of gaining first place."

After 11 Na4, Tal attacks Keres' bishop on c5, and Keres adds, "A new line, instead of the customary Rb1. With the text-move White plans to initiate the well known pressure on the c5 square after 11 ... Be7 by 12 Be3. Thus he would attain a position that would ensure him a lasting initiative without any danger of losing. Hence black chooses a different, perhaps riskier, continuation so as to lead the game away from the usual paths."

Keres retreats his bishop to b6, and after the exchange ends up with a rather ugly position of doubled b pawns and white with the 2-bishop advantage. There aren't many who would want to play black's position from move 11 needing a win against a strong white player. Rybka sees the position as .33 for White at this point.

Keres writes, "An essay at appreciating the position that has now arisen might seem at first glance to make it appear much more favorable for white than it really is. He enjoys the advantage of two bishops, controls the important d4 square, while his opponent's pawn position reveals marked weaknesses on the queen-side. But if one tries to suggest a plan by which white can increase his supposed advantage then one is pulled up sharp by unexpected difficulties. It becomes apparent that Black's position too contains various advantages that should not be underestimated."

Keres estimates that Tal's move 15 a3 is a mistake, "white overestimates his position and apparently imagines he can quietly increase his pressure in the center ... Something must of necessity be undertaken against the positional threat of 15 ... Bh6."