Review of Game 3: Lee Sedol's opening mistakes due to enormous mental pressure
After two successive losses, Lee Sedol is under extremely high pressure not to lose the entire five-game match with AlphaGo. Lee Sedol is heavily touched, very disappointed and feels particular anguish after the shock of his second loss. Both his confusion afterwards about why he had lost the game and the difficulties he had with his team tracing back any mistakes, showed also that AlphaGo played a nearly perfect game. So, is Lee Sedol able to win from a Go-program that plays virtually perfect?
With black 17, a rather complicated opening fight starts in the upper left corner (see Dia. 1). White's invasion inside black's influence is an attempt to reduce the black potential severely, without leaving a weak group that is easy to attack or giving black some advantages otherwise (for instance, to allow for much strength on the outside or territory on the inside).
Dia. 1: Game 3, after black 17 (circle, Lee Sedol is black)
Dia. 2: Game 3, after white 28 (circle, Lee Sedol is black)
AlphaGo responds underneath (circle in Dia. 3) to ensure the option to connect later or to be able to attack Lee Sedol later on. This move provides some life-air to the white group as well as possibilities to pressurize black's stones thereabout (triangle in Dia. 3).
Black really had to play first on this point (circle in Dia. 3, instead of triangle) to threaten to connect underneath himself (and keep white weak and separated). And if white then would have responded, black nevertheless would have had (in sente) the opportunity to play the triangle move. In short, a missed opportunity by Lee Sedol which immediately gives AlphaGo the initiative.
Dia. 3: Game 3, after white 36 (circle, Lee Sedol is black)
Dia. 4: Game 3, after white 48 (circle, Lee Sedol is black)
Obviously, white handles attacking as best defense. Even though white's upper left group is itself still in the danger zone, white is able to escape towards the center. And in case of emergency white can try to make eyes with forcing moves on black's upper left corner.
Dia. 5: Game 3, after white 70 (circle, Lee Sedol is black)
Dia. 6: Game 3, after white 78 (circle, Lee Sedol is black)
Also, white's upper left group is not yet entirely safe and still a significant burden white has to take into account. AlphaGo's response on Lee Sedol's counterattack is yet effective and cooperates optimally with all white's stones at the right edge. In addition, it's response provides opportunities in case white's group in the upper left later on needs support.
Dia. 7: Game 3, after white 90 (circle, Lee Sedol is black)
With 89 (triangle in Dia. 7) black connects more or less the two cutting stones on the right (on P8+9) and at the same time attacks the white group in the upper left. AlphaGo is alert and strengthens it's group immediately with 90 (circle in Dia. 7). It looks like that Lee Sedol should have played here himself first (threatens to cut, makes points and weakens the white group) in sente. However, AlphaGo succeeds in further simplifying the position as the white group in the upper left now has almost sufficient options to live.
Dia. 8: Game 3, after black 129 (circle, Lee Sedol is black)
However, AlphaGo stays very calm and plays sophisticated during Lee Sedol's invasion (triangle in Dia. 8). This move gives white a number of opportunities to connect the two white stones either to the left or to the right. Black again complicates the situation to threaten breaking through white's surroundings towards the center, or to capture the two white stones and try to live.
Dia. 9: Game 3, after white 148 (circle, Lee Sedol is black)
Dia. 10: Game 3, end stand after white 176 (circle, Lee Sedol is black)
Unfortunately, Lee Sedol is unable to force AlphaGo into any error, not even a single one. Using internal ko threats, AlphaGo triumphs (as the program already 30 moves ago had evaluated or computed). And after white 176 (circle in Dia. 10) there is no other option for Lee Sedol than to resign.
Kwon Kay-Yong, one of Lee Sedol's former coaches, told a news agency: "AlphaGo played consistent and well balanced from start to finish while Lee, as he is only human, showed some mental vulnerability". Thereby, Lee Sedol's great feeling of responsibility --towards all people that were watching over his shoulder and had such a great faith in him-- inevitably began to work against him.
According to Younggil An (8p) and David Ormerod, this third game demonstrated that "AlphaGo is simply stronger than any known human Go player. AlphaGo was seen to capably navigate tricky situations known as ko-fights that did not come up in the previous two matches". Ormerod added: "in the middle of a complex, all-or-nothing ko fight, AlphaGo displayed sufficient 'confidence' that it was winning the fight and simply ignored the ko and played a large move elsewhere".
During the post-game press conference, where hundreds of photographers exposed Lee Sedol to minutes-long dazzling flashlight, while the loss of the Google DeepMind challenging match was still hammering his mind with this third successive defeat by AlphaGo, Lee Sedol was visibly touched and deeply saddened: "I don't know how to start or what to say today but I think I would have to express my apologies first: I should have shown a better result and better outcome and better contents of the game played. I apologize about not being able to satisfy a lot of people's expectations. I felt powerless. If I would redo the match I probably would not have been able to win".
To continue: "I think it is fair to say that it beat Lee Sedol at his own game. What I see in AlphaGo is the potential when it plays new moves as it did in the 2nd game, it's potential to inspire Go players to perhaps study a different type of opening moves. I think we could have a revolution of the years coming up with AlphaGo helping us, giving us a boost to start it. I like to characterize today by my believe that the AlphaGo team created a true work of art".
And answering a journalist's question, Lee Sedol said: "Although AlphaGo is a strong program, I would not be able to say AlphaGo is a perfect program (not at the level of so called divine Gods). Yes, compared to humans it's moves are different and from time to time are superior but I do feel that there are weaknesses in AlphaGo's way of playing. Today was Lee Sedol's defeat but not a defeat of human beings".
Google and the Korean Baduk Association, who both organized this match, already agreed earlier on that the match would continue up to and including the fifth game in case the winner of the match would be known after three wins in a row.