Google’s AlphaGo program is playing against Lee Se-dol in Seoul. Mr Lee had been confident he would win before the competition started. The Chinese board game is considered to be a much more complex challenge for a computer than chess. Mr Lee is considered a champion Go player.
"AlphaGo played consistently from beginning to the end while Lee, as he is only human, showed some mental vulnerability," one of Lee’s former coaches, Kwon Kap-Yong, told the AFP news agency.
Go is a game of two players who take turns putting black or white stones on a 19-by-19 grid. Players win by surrounding their opponents pieces with their own. In the first game of the series, AlphaGo triumphed by a very narrow margin, Mr Lee had led for most of the match, but AlphaGo managed to build up a strong lead in its closing stages.
After losing the second match to Deep Mind, Lee Se-dol said he was "speechless" adding that the AlphaGo machine played a "nearly perfect game". The two experts who provided commentary for the YouTube stream of for the third game said that it had been a complicated match to follow. They said that Lee Se-dol had brought his "top game" but that AlphaGo had won "in great style".
The AlphaGo system was developed by British computer company DeepMind which was bought by Google in 2014. It has built up its expertise by studying older games and teasing out patterns of play. And, according to DeepMind chief executive Demis Hassabis, it has also spent a lot of time just playing the game.
"It played itself, different versions of itself, millions and millions of times and each time got incrementally slightly better – it learns from its mistakes," he told the BBC before the matches started.
This virtuous circle of constant improvement meant the AI went into the five-match series stronger than when it beat the European champion late last year. Two more games will be played in this match.