Following over three and a half hours of gameplay, Google DeepMind’s AlphaGo claimed victory over Go world champion Lee Sedol, of South Korea. Sedol conceded the match with 28 minutes and 28 seconds remaining on his clock.

The landmark match is the first in a series of five. The second is scheduled tonight at 11 p.m. EST.

An ancient Chinese game, Go is complex, so much so that an artificial intelligence system surpassing a human during gameplay at the champion level was thought to be at least a decade away.

That all changed in October 2015. Playing against three-time European champion Fan Hui, AlphaGo won 5-0 in a formal match.

Now, AlphaGo is facing a much more daunting challenge.   

After the match, DeepMind CEO and Founder Demis Hassabis took to Twitter and compared the win to landing on the moon.

“I don’t regret accepting this challenge,” said Sedol, according to The Verge, following the match. “I am in shock, I admit that, but what’s done is done. I enjoyed the game and look forward to the next. I think I failed on the opening layout so if I do a better job on the opening aspect I think I will be able to increase my probability of winning.”

Hassabis and colleagues published a paper in Nature regarding AlphaGo’s mastery of the game in January 2016. On top of defeating the human European champion, the researchers reported that AlphaGo bested other Go programs 99.8 percent of the time.

Match 2 can be watched on DeepMind’s YouTube channel. The matches are being held in Seoul, South Korea.