Teyss: Notes by Geller.
<4...Nf6> Keres, an expert in the Ruy Lopez, varies his system. A few rounds earlier, he played 4...d6 against Spassky and the game ended in a draw.
<8.d4> If 8.h3, after 8...Bd7 9.d4 Rc8 10. Ndb2 Bf8, the normal N move from d2 to f1 is hindered by the threat 11...exd4.
<8...Nd7?!> Better is 8...Bd7. (Keres already made this move twice against Fischer in Curaçao 1962, in a slightly different position: he lost the first game and won the second one.)
<9…Be3> More precise than the stereotyped 9.Nbd2 when Black can compensate for the tempo White saved by not playing h3: 9…Bf6 with the threat 10…exd4.
<10…Re8?!> Better give up the centre with 10…exd4 11.exd4 Nb6 12.dxe5. Also not good was 10…exd4 11.exd4 Nb6 12.Bc2 with a broken Pawn structure.
<11.d5> At the right time. The pinned Nd7 hinders development on the Qside, the Bf6 prevents counterplay with ...f5 and the f7 square is weak even if it's not obvious yet. All this is a consequence of Black's passive play in the opening with 8...Nd7.
<12.b4> Better than 12.c4 to which Black could have replied 12…c5. Now it’s impossible because of 13.Bxd7 and 14.bxc5.
<12…g6> If 12…Ng6, 13.g3 and it’s not clear what Black can do next.
<13.c4> I could have played 13.Rc1 first but I wanted to trigger 13…c6, else White can play c5.
<13…c6?!> (It’s surprising Geller puts “?!” after saying it’s necessary. The engine recommends 13…Rf8 with an inferior but solid position.)
<14…Bg7?> The position is lost. (This comment seems slightly exaggerated.)
<15.c5! dxc5> Withdrawing the BB on g7 has provided White an important tempo for the attack.
<18…Ne7> There are no good alternatives: 18…f6? or …Bf6 19.Ne4! or 18…Qa5 19.Nc4.
<20.Nd6! hxg5> If 20…Rf8 21.Bxc7 Qxe7 22.Nxc8 Raxc8 23.Qxd7.
<21.Nxf7!! Qa5> If 21…Kxf7 22.Nxg5+ Kf6 23.Nh7+ Kf7 24.Bb3+ or 22.Kg8 23.Qb3+ Kh8 24.Qh3+. If 21…Qc7 22.N7xg5 with the threat 23.Bb3+.
<23.Bxd7> Simplest: White gets the material back with a strong attack.
<24…Qa3> After 24…Qd5? 25.Rd2, the BQ is trapped.
<25…Qb4> 25…Qa2 also loses the Q: 26.Rc2 Qd5 27.Rd3.