"Though I have a lot of experience in Go I have never felt before such severe pressure as I do now, and I suppose my abilities were a bit lacking to overcome that."Lee resigned after more than four hours of play in the game against Google's computer program AlphaGo.

　　The five-game match has been regarded as a representative fight between human brains and artificial intelligence.

　　李世石聊围棋人机大战

　　Although losing for a third time, the 33-year-old grandmaster still thinks it is "not a defeat for humans".

　　"AlphaGo shows the part of its weaknesses, so I doubt whether it has skills that can actually deliver a message to humans. Therefore, I think Lee Sedol is the one who lost today, not humanity."Go is a popular game in countries such as China, South Korea and Japan.

　　It involves two contestants moving black and white stones on a square grid, with the aim of seizing the most territory.

　　Demis Hassibis, founder of Google subsidiary DeepMind which designed AlphaGo, is a bit surprised that the artificial intelligence program beat one the world's top Go players.

　　"To be honest, we are a bit stunned and speechless. Lee Sedol put up an incredible fight again, AlphaGo made a large territory at the bottom of the board, but Mr. Lee found some really amazing tactics to play in the territory and create a really huge co-fight."Google executives have revealed that AlphaGo has sought to approximate human intuition, by studying old matches and using simulated games to hone itself independently.

　　China's top Go player Ke Jie has earlier said that he would like to take on AlphaGo.

　　But now he thinks the computer program might not be an easy opponent after all.

　　"Sooner or later, the computer will defeat all human Go players. I am actually quite worried about that because I don't know how to face it when the time comes. I hope we can do something to stop Alpha from learning so fast and I will try to get him to slow down a little bit on the road of dominating the Go world."The five-game match, which kicked off on Wednesday, will last until next Tuesday.

　　The next match will be played later this Sunday in Seoul.