Then he smiled and began outmanoeuvring his foe. “I can’t lose,” Hikaru Nakamura, 32, said to the exultant onlookers. Victory seemed close as members of the opposing army were vanquished one by one. “I win again — there you go, guys. Wow.” Nakamura gave himself just a moment’s respite, then plunged into another fray. Pawns, knights, bishops and even kings fell before him as the chess grandmaster demolished a slate of online challengers, all while narrating the tide of the battle to tens of thousands of fans watching him stream live on Twitch, the Amazon-owned site where people usually broadcast themselves playing video games like Fortnite and Call of Duty.