The machines this week triumphed over man, as Google DeepMind's artificial intelligence (AI) took on the top – and very human – player in the ancient chess-like Chinese game of Go, winning three of their matches.
However, the fourth bout between them has reversed the tables and resulted in Lee Sedol triumphing over AlphaGo for the first time.
The technology "pressured AlphaGo into a mistake that it couldn't recover from" according to the man behind DeepMind, Demis Hassabis.
Lee Sedol wins game 4!!! Congratulations! He was too good for us today and pressured #AlphaGo into a mistake that it couldn’t recover from— Demis Hassabis (@demishassabis) March 13, 2016
Lee Sedol is playing brilliantly! #AlphaGo thought it was doing well, but got confused on move 87. We are in trouble now…— Demis Hassabis (@demishassabis) March 13, 2016
Mistake was on move 79, but #AlphaGo only came to that realisation on around move 87— Demis Hassabis (@demishassabis) March 13, 2016
The resignation of AlphaGo was greeted with applause from the audience.
While AlphaGo has already triumphed in the best of five tournament, it's a victory for anyone worried about AI taking over completely and a sign that machines are still fallible – just perhaps not as much as humans.
Sedol had gone into the match confident of victory over the technology, but after losing sounded regretful about the overall loss.
"I don’t know how to start or what to say today, but I think I would have to express my apologies first. I should have shown a better result, a better outcome, and better content in terms of the game played, and I do apologise for not being able to satisfy a lot of people’s expectations. I kind of felt powerless," Sedol said at a press conference after the third match.
Hassabis said AlphaGo resigns after the probability of winning falls below a certain threshold, speaking at a press conference following the match.
But, it was Sedol's very human perseverance – despite zero chances of winning the tournament after the third AlphaGo win – which led to today's triumph.
A fifth and final game will take place on Tuesday when Sedol will attempt to balance the final score more evenly to two wins against AlphaGo's three.