A master player of the game Go has won his first match against a Google computer program, after losing three in a row in a best-of-five competition.
Lee Se-dol, one of the world’s top players, said his win against AlphaGo was “invaluable”.
The Chinese board game is considered to be a much more complex challenge for a computer than chess, and AlphaGo’s wins were seen as a landmark moment for artificial intelligence.
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.
Commentator Michael Redmond said AlphaGo had been playing well up until the middle of the game, but at move 78, Mr Lee played brilliantly.
Speaking after his victory, Mr Lee said: “I’ve never been congratulated so much because I’ve won one game.”
Google representatives said the defeat was “very valuable” for AlphaGo, as it identified a problem which they could now try to fix.
A fifth game will be played on Tuesday.