Google’s AlphaGo computer is two ahead in its five-game match of wits against the world champion of the ancient Chinese game of Go, leaving the human competitor “speechless” and the designer behind the machine surprised.

Lee Se-Dol said he was in shock at losing to a machine after it beat him in the first game on Wednesday. On Thursday, after losing the second contest, he said he could not identify a weakness in AlphaGo, saying: “At no time did I feel that I was leading, and I thought that AlphaGo played a near-perfect game.”

Demis Hassabis, chief executive of Google DeepMind, the London-based unit behind AlphaGo, tweeted his surprise immediately after the victory. “AlphaGo wins match 2, to take a 2-0 lead! Hard for us to believe,” he said. “AlphaGo played some beautiful creative moves in this game. Mega-tense.”