Lee Sedol | Player Profile | PlayGo.gg

The man who beat AlphaGo

Biography

Lee Sedol (born 1983) turned professional in 1995 and was the most feared attacking player of his generation. Between 2002 and 2012 he won 18 international titles, a total second only to Lee Changho.

In March 2016 he played the five-game match against DeepMind's AlphaGo. He lost 1-4, but his win in game four, sparked by the famous wedge at move 78, remains the only game a human has won against the program in a formal match.

His rivalry with Gu Li defined a decade of Korea-China Go, including the 2014 ten-game match that Lee won 6-2. He retired from professional play in November 2019.

vs. AlphaGo, Google DeepMind Challenge Match, Game 4

March 13, 2016

Down 0-3 in the series and behind on the board, Lee Sedol took White and wedged at move 78, a move Gu Li called divine on the Chinese broadcast. AlphaGo's evaluation collapsed and it began playing nonsense moves; it resigned at move 180. This remains the only game a human has won against AlphaGo in a formal match.

KataGo does not think the wedge at 78 worked. Lee's winrate barely moved, from 3% to 4%. What followed did the damage. AlphaGo's 89 lifted Lee to 37%, and after his J11 on move 92 the reply S9 on move 93 took him to 67%. P7 would have held for Black, a move 15% of 9-dan players find, and AlphaGo did not.