It is said that △P*66 was losing move for gote at #102 because sente had the decisive attack at that moment.
|The position at #101|
At first, challenger Toyoshima had been thinking △P*71 and △G-32 as candidate moves.
But, in the case of △P*71, after calculation with ▲G*53 △N*85 ▲+Rx92 △Lx ▲R-62 △K-23 ▲S*22 △P-25 ▲Px △+Bx ▲P*26 (Diag.1), he couldn't have any confidence in the position.
And, in the case of △G-32, it proceeds to quite complicated positions.
After calculation with ▲N-82+ △Sx68 ▲Gx △G*78 ▲Gx △Sx+ ▲Kx △B*69 ▲K-67 △B-58+ ▲K-66 △+B-46 (Diag.2) ▲S*31 △K-23 ▲N*15 △Px ▲G*22 △K-13 ▲S*14 △+Bx ▲Px15 (Diag.3), he was not sure which side was winning at Diag.3, and then finally evaluated the position as not good for gote. Thus, although he chose △P*66, as the result, △P*66 became a losing move. Habu considered the position as a very close game.
The sequence from ▲S*31 to ▲Px15 is the technique for removing the threatmate and giving a threatmate to the opponent's king reversely. The other ways for gote to deal with the check would lead to a checkmate.
At first glance, you may think sente is winning at Diag.3. But, after this position, a lot of variations still exist. They are written in detail on the website. Please check it out.