Tic tac toe perfect play: how to never lose

Tic tac toe has nine squares and eight winning lines, which makes it small enough to solve completely. The result of that solution is worth internalising: with correct play from both sides the game is a draw, and every win you have ever had came from an opponent stepping out of the correct line somewhere.

This guide covers both halves of the game—how to be unbeatable, and how to punish mistakes—using the boards at easy, medium, and hard difficulty as practice.

Why the game is drawn

There are only 255,168 possible games, and after removing symmetry and illegal moves the number of distinct positions is small enough that every one has been evaluated. The conclusion: the first player can guarantee at least a draw, the second player can guarantee at least a draw, and neither can guarantee a win.

The reason is that the board fills before a competent attacker can build two unstoppable threats. Blocking is cheap when there are only nine squares, so defence always keeps up—unless the attacker creates a fork, which is where all the interesting play lives.

Open in the centre

The centre square belongs to four of the eight winning lines: the middle row, the middle column, and both diagonals. A corner belongs to three, and an edge belongs to only two. Opening in the centre maximises the number of ways your first mark can matter.

The centre opening is also the safest. If the second player answers anywhere incorrectly, you have more immediate follow-ups available than from any other opening, and if they answer correctly you are already on the drawing line.

If you open in a corner

A corner opening is the aggressive choice, because it sets up forks faster—if the opponent answers on an edge rather than in the centre, you can build two threats immediately and win in four moves. This is the standard punishment for a weak reply, and it is why beginners who open in a corner win more games than beginners who open in the centre.

Against a correct reply (the centre), a corner opening still draws. So the corner is higher variance: more chances to win quickly, no additional risk of losing, provided you recognise when the fork is available.

The fork: the only way to win

A fork is a position where you threaten two lines at once, so the opponent can block only one and you complete the other on your next turn. Every tic tac toe win is a fork. There is no other mechanism.

The classic shape: X in the centre and a corner, O blocking elsewhere, X in the opposite corner. X now threatens a row and a diagonal from that second corner. O can stop one; X takes the other. Recognising this shape before it is complete is the whole skill of attacking tic tac toe.

Defending against a fork

When your opponent has two marks and you have one, you are usually one move away from being forked. The correct response is not to block the visible threat—it is to occupy the square from which they would create the second one.

A reliable heuristic: if they have two in a row and it is your turn, look for the cell that would give them two separate two-in-a-rows. Take that cell. Blocking the existing line instead is the mistake that loses the game.

Playing against each difficulty

Easy blocks immediate wins and takes its own, but does not look ahead—so opening in a corner and building a fork reliably wins. The goal here is to practise seeing the double threat before it exists.

Medium defends more consistently but does not order its moves exhaustively, so quiet setup moves still work. This is the best difficulty for learning to create a fork without telegraphing it.

Hard plays perfectly. You cannot beat it—you can only draw, which is itself a useful check on your defence. If you lose to hard mode, you made a fork-creation mistake somewhere; if you draw every time, your blocking is sound.

A summary

1. Open in the centre, or in a corner if you want fork chances.
2. Block any line that is about to complete.
3. Before blocking, check whether they are setting up a fork and take the forking square instead.
4. Attack only by creating two threats at once.
5. Expect a draw against a correct opponent—and take it as a good result.

Where this pattern appears elsewhere

Forks are not unique to tic tac toe. The same double-threat mechanic decides Connect Four, where the board is larger but the principle—create two problems with one move—is identical. Our Connect Four strategy guide works through the same idea on a 7×6 grid.

Frequently asked questions

Play it on Gaming Onion

• /games/tic-tac-toe
• /games/tic-tac-toe/hard