SEOUL, South Korea — Google’s Go-playing software defeated a human champion for the third straight time Saturday to clinch the best-of-five series and establish its superiority in an ancient Chinese chess-like game long thought to be the realm of humans.

South Korea’s Lee Sedol, one of the world’s best Go players, remained winless against AlphaGo, Google DeepMind’s artificial intelligence machine, after another close match in Seoul. Despite losing the series, Lee is scheduled to play twice more against AlphaGo, on Sunday and Tuesday.

The highly anticipated showdown between human and machine has crushed the pride of Go fans, many of them in Asia, who believed Go would be too complex for machines to master. Some thought it would take at least another decade for computers to beat human Go champions.

Many top Go professionals commented that AlphaGo displayed unorthodox, questionable moves that initially befuddled humans but made sense in hindsight.

Lee looked shaken in the post-match news conference, apologizing to his fans for what he said was a “powerless display” against the game-playing machine.

He said he felt extreme pressure heading into the third match, but that with the series now decided, he might have a better chance in the final two matches because “the psychological part matters to humans.”

Google co-founder Sergey Brin, who was in Seoul to watch the third match, described Go as a “beautiful game” and said he was excited that the company has been able to “instill that kind of beauty in our computers.”

In Go, which is considered to be far more complex than chess, two players take turns putting black or white stones on a 19-by-19 square grid. The goal is to put more territory under one’s control by surrounding vacant areas with the stones.