Lee Sedol, a professional player of the Chinese board game Go, apologized Saturday after a Google computer programme won its third straight match, ensuring the artificial intelligence (AI) software of victory in the landmark five-game machine-versus-human contest.
The AlphaGo programme beat the South Korean world champion after more than four hours of playing the ancient game in Seoul, seen as one of the biggest tests of the power of artificial intelligence.
"I want to express my apology. I was not able to meet people's expectations," Lee said after the third match.
"I felt powerless. But today's defeat was Lee Sedol's defeat, not the defeat of humankind," said the world champion.
Demis Hassabis, co-founder of Google's DeepMind AI branch which created AlphaGo, praised Lee Sedol as "an astonishing genius" in spite of the champion's loss.
The five-game contest will continue for two more games, in spite of AlphaGo's unbeatable 3-0 lead. Following Lee's defeat, the competition's prize money of 1 million dollars will be donated to charity.
AI systems had long struggled to beat humans at Go, which was previously thought to be too complex for computers, as they lacked the self-learning software needed to adapt to the millions of possible gameplay scenarios.
"It won't be long before AlphaGo beats all human players," Hassibis said.
The rules of Go, which originates in China, are easy in principle: two players try to conquer spaces with white and black stones on the board, which is divided by vertical and horizontal lines into a grid.
AlphaGo was developed by Google's DeepMind team to forecast the most probable moves of its human opponent and adjust itself accordingly.
In October, the programme won a five-game match against Fan Hui, a top European player, ranked well below Lee internationally.