Concepts

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The following game illustrates an unusually long yoritsuki sequence, though it starts in a manner that will be familiar to all grades of player, and so you can easily become alert to the possibility of playing this way.

White was the late Kato Masao. He was playing O Rissei in the Ryusei, which means this was a relatively quick game.

The bit that mainly interests us started at White 114. White has just ignored Black's endgame move in the upper left, which is White's only substantial territory. It may seem folly to let Black take a chunk out of that, but if White defends there and tries to match territories, he is in danger of losing heavily.

White instead preferred to exploit the strength of his position (he assumes he has no weak groups Black can attack) and the fact that he has sente which he can use to poke and prod at Black. However, according to Takemiya, White was arguably a little rash in assuming he had no weaknesses. His group in the lower right can come under attack. Black could have tried to exploit that (and thus the thinness above) by connecting at 136 rather than 135. Instead, with 136 to 140 White got his first real profit from the yoritsuki (capture of three stones), and was able to grind on with sente, sente, sente and tiny gains until he had properly secured his lower-right group, and was then able to go back to 164 - 51 moves later! - having satisfied himself he was now ahead. 164, in other words, was a declaration of victory. The coup de grâce was 188, capture of another three stones thanks to the earlier yoritsuki, and that was the last move in the published record, though play actually continued for a while on TV.

Other comments you may find helpful when you play over the game:

The joseki in the lower left had recently become a popular pattern. White chose to build up his position by laying out staking posts (kamaeru - another concept that needs exploring more in English). Takemiya Masaki commented that, instead of 20, White could have continued by pressing to the right of 16, building a solid wall rather than banging in a few posts for a future fence. We see there a glimpse of Takemiya's style, but either way a moyo is likely to emerge in the upper left (of different types, mark you). But O Rissei played 25 precisely because he has a dislike of moyo games and so he entrenched himself before one could emerge.

White (Kato) patiently opted for thickness (strength) with 28 and 34, letting Black settle himself with 35 to 43. White 50 was another stylistic turning point. He could have approached on the other side. Takemiya was not too impressed by 59. He preferred extending to 60. The result of the choice in the game was that White got to attack at 68. At this point the game in in danger of slipping away from Black. Still, although White gets good shape with 78 to 82, Black can counterattack at 83. At this stage, however, O Rissei was in byoyomi (one minute a move) and missed the sharpest way to proceed (which, after White 96, was at 98 - he had expected White to answer at 104 or similar). He realised he'd muffed it as soon as he played 97.

The full game in sgf form: