How an AI took down four world-class poker pros

That was anticlimactic," Jason Les said with a smirk, getting up from his seat. Unlike nearly everyone else in Pittsburgh's Rivers Casino, Les had just played his last few hands against an artificially intelligent opponent on a computer screen. After his fellow players -- Daniel McAulay next to him and Jimmy Chou and Dong Kim in an office upstairs -- eventually did the same, they started to commiserate. The consensus: That AI was one hell of a player. The four of them had spent the last 20 days playing 120,000 hands of heads-up, no-limit Texas Hold'em against an artificial intelligence called Libratus created by researchers at Carnegie Mellon University. A similar scene had unfolded two years prior when Les, Kim and two other players decisively laid the smackdown on another AI called Claudico. The players hoped to put on a repeat performance, finish up the event on January 30th, and ride the rush of endorphins until they got home and resumed their usual games of online poker. The fight wasn't even close. All told, Libratus won by a more than 1.7 million (virtual) dollars, and just like that, the second Brains vs. AI competition came to a close. To understand what these players were up against and what makes Libratus work, let's go back to a time before all hope of victory was lost. For the four men playing against Libratus, victory didn't always seem impossible. The AI was in the lead from the get-go, building an impressive streak of wins for the first three days. Day four saw the gap narrow by $40,000, and a string of successes on day six brought the humans to within $50,000 of the lead. "In the start here, we lost the first day," Les explained. And then we were losing, but then we fought back up to nearly equal. We were feeling really confident! We know how to play, we're going to be able to win."