zydeco: An interesting matchup between a 'right player' (Portisch) and a 'wrong player' (Larsen). Portisch actually had Larsen's number for most of their career, but this game is a bit like Larsen vs Portisch, 1964 when Larsen completely wrongfooted Portisch.
Larsen comments on move 2: "Against Portisch it is probably wise to play such an old fashioned opening. He knows a great deal of theory and feels at home in those openings. It is my impression that he feels uncomfortable in "museum openings."
Both players agree that Portisch should have played 11....Ne3 12.Bxe3 Bxe3 13.Qg3 Nd4 with equality. Portisch says that he overestimated his chances and tried for a win with 11....Nf6.
Portisch thinks he should have played 12....d5 13.exd5 Nb4. If then 14.Kd1 e4! If 14.fxe5 Qxe5 15.Kd1 Nbxd5 16.Re1 0-0 with a wild position.
The book on Portisch at this point was that he reacted nervously whenever a game suddenly became wild -- and Poritsch plays into that by avoiding the wild line for a 'safer' but inferior variation with 12....Na5.
Portisch says that he missed 17.c3! after which white's superiority is evident.
On move 29, Larsen writes: "Must I tell the truth and nothing but the truth? Well, the spectators were very noise every time Fischer or Petrosian made a move, and it was very difficult to concentrate. Here I realized that in my calculations I had overlooked something very simple. If 29.Rxg6 Rxg2! I took some time to overcome the shock and study all the calculations carefully, and, for the 10th or 15th time in this game the most straightforward line turned out to be the best."
Larsen comments on the ending that "black's position is hopeless, but in some variations only one tempo is missing!"