Google's computer program AlphaGo has been dominating in the middle of the third of a historic five-game Go match with South Korean Lee Sedol, the world champion of the ancient Chinese board game who lost his first two matches.
The third match, which is seen as a representative match between humans and artificial intelligence (AI), began at 1 p.m. local time (0400GMT) on Saturday at Four Seasons hotel in Seoul.
The "century of the match" between Lee and AlphaGo, a computer program developed by Google's London-based AI subsidiary DeepMind, will run through next Tuesday after an opening match on Wednesday.
Commentators said AlphaGo is dominating in the middle of the match as the computer program effectively defended Lee's aggression in an early phase.
Lee is seeking to invade into large groups of white stones set up by AlphaGo, keeping his aggressive style of playing. The human champion turned aggressively after his consecutive losses in the first two games, commentators said.
Playing Black, Lee put his starter at the upper-right flower spot, placing his next marker at a position right beside the upper-left flower.
AlphaGo started off the game, with the first two white stones placed both on flower positions, a strategy seen in the first match.
The human champion entered into an aggressive battle from the very beginning to dominate the game in the first half.
Following his second defeat, Lee told a press conference on Thursday that his winning possibility would likely rise if he gets dominant in the first half.
The 33-year-old champion allegedly analyzed AlphaGo's strategy all night after the second loss with his South Korean Go professional colleagues, reaching a conclusion that he can win only when he dominates in an early phase.
Lee has lowered confidence in his victory over the historic match. During the Feb. 22 press conference, he said AlphaGo would by no means win any game, but he got less confident about a 5-0 victory Tuesday, a day before the opening match.
Lee expected a 50-50 victory after this first defeat on Wednesday. He reduced his confidence further on Thursday, saying that he would do his best to win at least one game.
One commentator said that AlphaGo showed "innovative, adventurous and dangerous-looking moves" in the first two matches, noting that the computer program seemed to get more confident in the latter half.
The AI boasts of a deep learning capability to learn for itself and discover new strategies by playing games against itself and adjusting neural networks based on a trial-and-error process known as reinforcement learning.
Lee is regarded as one of the greatest Go players in the world as he won 18 world championships for 21 years of his professional career. He recorded a winning rate of about 70 percent with 47 victories in professional matches, while AlphaGo posted a 99.8 percent rate with hundreds of victories and only one loss.
Go, known as weiqi in China and Baduk in South Korea, originated from China more than 2,500 years ago. It involves two players who take turns putting markers on a grid-shaped board to gain more areas on it. One can occupy the markers of the opponent by surrounding the pieces of the other.
