SEOUL • A South Korean Go grandmaster has scored his first win over a Google-developed supercomputer in a surprise victory after three humiliating defeats in a high-profile showdown between man and machine.

Mr Lee Se Dol yesterday beat AlphaGo after a nail-biting match that lasted for nearly five hours - the fourth of the best-of-five series, in which the computer clinched a 3-0 victory on Saturday.

Mr Lee, 33, struggled in the early phase of the fourth match but gained a lead towards the end, eventually prompting AlphaGo to resign.

"Lee Se Dol was an incredible player and was too strong for AlphaGo," said Mr Demis Hassabis, head of the AlphaGo developer Google DeepMind.

"It was doing well... but then, because of Lee's fantastic play, it was pressurised into some mistakes," he said, describing the loss as a "valuable" way to fix the problems with the supercomputer.

Go involves two players alternately laying black and white stones on a chequer board-like grid of 19 lines by 19 lines. The winner is the player who manages to seal off more territory.

On the 78th move, Mr Lee placed a stone unexpectedly in the middle section of the board, confusing the AlphaGo.

Mr Hassabis tweeted that the AlphaGo made a "mistake" on the next move and only realised it several moves later.

Prior to the matches with Mr Lee, AlphaGo has played millions of games against itself to figure out the game and hone its tactics through trial and error. Their final game will be held tomorrow.

AGENCE FRANCE-PRESSE, BLOOMBERG