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I have been told that it is possible to guarantee no worse than a tie in normal 3x3 tic-tac-toe, but that the first move is very important. What is that important first move?

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Tic-tac-toe has been solved. The optimal first move is to go in the corner.

As always, there is a relevant xkcd. xkcd tic tac toe

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  • $\begingroup$ This is actually the most comprehensive answer yet. Wish I'd thought of it. $\endgroup$ – Xynariz May 14 '14 at 22:16
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    $\begingroup$ @Xynariz: Oddly, you did think of it first according to the timestamp on this comment; that diagram is in the link you provided. $\endgroup$ – blunders May 15 '14 at 2:48
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    $\begingroup$ I'm a bit sorry for 'stealing' the accepted answer like this. Using xkcd is a surefire way to get a high scoring answer. $\endgroup$ – SQB May 15 '14 at 7:27
  • $\begingroup$ I didn't accept the answer because it was from XKCD, I accepted it because it is the most complete answer, followed (currently) by Kendall's. $\endgroup$ – Xynariz May 16 '14 at 2:04
  • $\begingroup$ As much as I like everything xkcd does, this particular visualisation is actually a bit hard to read, if you were going to try to use it for strategising. $\endgroup$ – Trejkaz Nov 20 '17 at 4:48
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The first move can be made anywhere without sacrificing the game. If the opponent plays perfectly, any first move leads to a draw.

However, if the opponent does not play perfectly, then the optimal place to go is the corner, since that leaves only one spot (the center) for the opponent to go to get a draw, increasing their chance of making a mistake.

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    $\begingroup$ Also, even if they do go in the center, you can go in the opposite corner and if they play in a third corner you win, also. $\endgroup$ – durron597 May 14 '14 at 21:52
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    $\begingroup$ You could also add that, since you are obviously playing against a human, you should keep changing your starting position (not going for the corner every time) so that the opponent takes more time to learn the perfect strategy. $\endgroup$ – ghosts_in_the_code Apr 19 '15 at 15:58
  • $\begingroup$ @kendall frey Why the corner - do you have any references? $\endgroup$ – Ant Kutschera Apr 7 '18 at 21:09
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If you're first: Go in a corner.

If you're second, and the first person went in a corner: Go in the middle.

From both of these positions, it is possible to guarantee no worse than a tie.

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    $\begingroup$ It would be nice seeing the data to back this up. $\endgroup$ – IQAndreas May 14 '14 at 21:45
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    $\begingroup$ en.wikipedia.org/wiki/Tic-tac-toe#Strategy $\endgroup$ – Xynariz May 14 '14 at 21:57
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    $\begingroup$ To guarantee no worse than a tie, the first move makes no difference. It's the second move that's important. $\endgroup$ – Michael Myers May 21 '14 at 5:14
  • $\begingroup$ Wikipedia does not say that starting in the corner is best. $\endgroup$ – Ant Kutschera Apr 7 '18 at 21:10
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There is a nice article analyzing the Tic Tac Toe first move strategy at https://paperandpencilgames.com/2019/02/tic-tac-toe-strategy-tutorial.html

To address the reviewers comments, here is the conclusion of the article. There is no way of winning against a "perfect player". Choosing a corner as the first move gives you the best chance of winning against a less experienced opponent. Even if your opponent is a "perfect player" you can still tie the game.

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    $\begingroup$ I am new to this site. Thank you for your reviews. I updated my answer to address your comments. $\endgroup$ – Domosed Feb 8 at 18:53
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One way to answer this is to consider all 255,168 possible games of tic-tac-toe and record if they result in a win, draw or loss for the starting player and analysing where the first move was for each of those games. According to such an analysis, opening in the centre is best, in this case.

Taking it a step further, about 90% of those games are "stupid" because they include moves where players either miss the chance to win immediately or they miss blocking the opponent who can win in their next move. If you disregard those games, then the best opening move becomes a question of how you define "best". If you consider the number of winning games that there are after opening, then an edge opening is best. If you want to avoid drawing or losing, then the center is best. You can combine those results, say weighting winning with a factor of one hundred, drawing with a factor of 10 and losing with a factor of -1. This results in the center again being the best place to start.

In contradiction to most of the answers here, starting in the corner is hence not the best move, when using the number of games that can be played from an opening move as an indicator of what is "best".

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