The unorthodox contest marked the latest highly marketed man-versus-machine challenge. In 1996, IBM created a computer system that beat a chess grandmaster for the first time. In 2011, its Watson supercomputer defeated two record-winning Jeopardy! contestants. And Alphabet Inc.’s AlphaGo famously proved AI can master the ancient and intricate game of Go. But debating — which requires creativity and emotive elocution — has proven more elusive.