Deep Thought Beats a Grandmaster, 1988
In November 1988, at the Software Toolworks Championship in Long Beach, California, a chess computer called Deep Thought, the direct predecessor to IBM's Deep Blue, defeated Grandmaster Bent Larsen. It was the first time a computer had beaten a grandmaster under real tournament conditions, not an exhibition or a specially arranged match, and it happened nine years before Deep Blue's famous 1997 win over Garry Kasparov.
Why this result, not 1997, was the real turning point
Deep Blue's win over Kasparov gets all the attention because of who lost, but Deep Thought beating Larsen is arguably the more important structural milestone: it proved a computer could beat elite human opposition in a normal, rated, competitive event, with no special conditions attached, rather than in a bespoke exhibition match built specifically around the machine.
The game itself
The game was played as an English Opening, King's English Variation, a flexible, strategically rich structure that gave neither side an immediate tactical edge to calculate around, exactly the kind of position where a strong human's positional judgment was assumed to hold the advantage over a machine's brute-force search. Deep Thought tied for first place in the event overall, alongside Grandmaster Anthony Miles.
What Deep Thought actually was
Deep Thought was a Carnegie Mellon research project, evaluating on the order of a few hundred thousand positions per second, primitive next to what followed but built on the same core idea, deep brute-force search paired with a hand-tuned evaluation function, that its successor Deep Blue would scale up dramatically. Deep Thought went on to win the 1988 North American Computer Chess Championship and the 1989 World Computer Chess Championship before losing both games of an exhibition match against Kasparov later in 1989.
The gap this result exposed
Larsen was a genuine elite grandmaster, not a token opponent, and losing to a machine under real conditions forced the chess world to take computer chess seriously years before Kasparov ever sat down against Deep Blue. The story most people remember starts in 1997; the actual turning point, when computers stopped being a curiosity and became a real competitive threat, starts here.
Try it yourself
Play through the King's English above and notice how few forcing lines exist this early, this is a position judged on long-term structural factors, not tactics. That is exactly the terrain human players were supposed to own in 1988. Study a few of your own slower games and ask whether you are actually out-planning your opponents in quiet positions like this one, or just reacting to whatever is immediately in front of you.