ROUND TWO: Google's DeepMind AI just beat a human Go champion for a second time
The AlphaGo software played Lee Sedol in South Korea on Thursday, in the second of a series of five planned matches.
It was a closely fought game, with both players going into overtime.
The games are a significant milestone for AI research. Go is a simple game but has been notoriously difficult for computers to master because of the sheer number of potential moves. While AI programs began being able to beat human champions at chess decades ago, the best Go players in the world have always been able to outsmart Go-playing software - until now.
If you're not familiar with Go, it's a two-player turn-based strategy game. Each player puts down either black or white stones in an attempt to outmaneuver and surround the other player. It's easy to pick up but takes years to master.
AlphaGo won the first game On Wednesday after Lee Sedol resigned after 186 moves.
Before the first game, Lee Sedol had said he was "confident" about his prospects, telling reporters he was aiming for a 5-0 victory across all the games. But there's now a real possibility that AlphaGo could win every game.
The contenders need to win at least three games to win the Challenge Match. Victory for AlphaGo is now in sight.
This story is developing...