Tic-Tac-Toe Strategy: Every Opening Explained
Tic-Tac-Toe has three kinds of first move: a corner, the centre or an edge. All three are draws with perfect play, but they differ in how many replies lose. Against a corner, 7 of the 8 replies lose and only the centre holds. Against the centre, the 4 edge replies lose. Against an edge, 4 of the 8 replies lose. Every win comes from a fork, and every safe defence stops one before it forms.
The three openings at a glance
By symmetry there are only three different first moves: the four corners are the same move turned around, and so are the four edges. We checked every reply to each one with a minimax program, the same kind of full search Hop the frog uses on Hard, and sorted the replies into the ones that hold a draw and the ones that lose against correct play.
| X opens in… | O replies that hold the draw | O replies that lose |
|---|---|---|
| A corner | The centre (1 of 8) | All 7 others |
| The centre | Any corner (4 of 8) | Any edge (4) |
| An edge | The centre, the two corners beside X, or the opposite edge (4 of 8) | The two edges beside X, or the two far corners (4) |
So the corner is the best practical opening: it's just as safe as the centre, and it leaves your opponent the narrowest path. If you go second, the table is your whole defence plan in three lines. This guide walks through each opening in turn. For the short version, see how to win Tic-Tac-Toe every time.
Corner opening: how the wrong replies lose
Every losing reply to a corner goes down the same way: X makes a threat, O is forced to block, and X's next move threatens two lines at once. Two examples you won't see in most guides:
The other losing replies work the same way. Against the opposite corner, X takes a third corner, forces a block on the edge between, and forks with the last corner. Against an edge beside X, X takes the centre, forces a block in the far corner, and forks along the side.
As O, the corner opening is simple: take the centre, every time. Then, if X takes the opposite corner, answer with an edge, never a corner.
Centre opening: the corner reply and a mirror-image trap
If X starts in the centre, O must answer in a corner, and that holds the draw. X's most testing follow-up is the opposite corner. Now the advice flips: in this position O has to take another corner. Any edge loses.
Compare this with the corner opening, where O sits in the centre between two X corners and must play an edge. The positions look alike, but who owns the centre decides the right answer. The test is the same in both: after your move, can X make a move that blocks you and creates two threats? If yes, pick a different square.
Edge opening: rare, and that's the danger
Hardly anyone opens on an edge, so hardly anyone knows the answer. Half of O's replies are safe: the centre, either corner touching X's mark, or the edge directly opposite. The other half lose, and the two that feel most natural, the edges right next to X, are among them.
The same three moves (corner, forced block, centre) also beat a reply in either far corner. That's worth remembering as X: an edge opening is a decent surprise weapon against someone who only knows the corner and centre rules.
Forks: how every game is won
A fork is a single move that leaves you two lines that each need one more mark. Your opponent can block one, so you finish the other. In a game between two careful players, a fork is the only way anyone ever wins.
Forks come from squares that sit on many lines. The centre is on 4 of the 8 lines, each corner on 3 and each edge on only 2, which is why nearly every fork uses the centre or two corners. Look back at the diagrams: each winning X5 sits where two of X's lines cross.
The other ingredient is the forcing move. A fork needs two free moves to set up, and your opponent gets a turn in between. A threat solves that: it makes their reply for them, and it puts their mark on a square that doesn't spoil your plan.
How to stop a fork before it happens
Blocking a line of two is easy to remember. Spotting a fork one move early is the real defensive skill. When your opponent could fork on their next move, you have two ways out:
- Take the fork square yourself, if there's only one.
- Make a threat of your own that forces them to block on a square that is not a fork square for them.
The second one has a catch. In the corner, centre, opposite-corner position, O taking a corner does make a threat, but X's forced block lands on the last corner, which is exactly the fork square. X blocks and forks in the same move. An edge threat instead forces X onto an edge, where it does nothing.
A checklist that never loses
Run through this list before every move and take the first one that applies. We tested it against every possible sequence of opponent moves, playing both first and second, and it never lost a game.
- Win: complete your own line of three.
- Block: stop their line of two.
- Fork: make two threats at once.
- Stop their fork: take the fork square, or make a threat whose block isn't a fork square for them.
- Centre, if it's free.
- The corner opposite one of theirs.
- Any free corner.
- Any free edge.
Practise the openings against Hop
In GameLake's Tic-Tac-Toe you play the bamboo X and Hop plays the orange rings, and the first move swaps after every game, so you practise both sides of each opening. On Easy Hop makes a random move more often than not, and on Medium about one move in four is a random one, so those levels are where the traps in this guide pay off. Hard searches every position, so a draw there means you defended perfectly. You can also pick 2 players to try the edge opening on a friend.
Frequently asked questions
What is the best opening move in Tic-Tac-Toe?
A corner. It draws with perfect play like every opening, but 7 of the 8 replies lose, so it gives your opponent the most chances to go wrong.
What should you do if your opponent takes a corner first?
Take the centre. It's the only reply that doesn't lose. If they then take the opposite corner, play an edge, not a corner.
What should you do if your opponent starts in the centre?
Take a corner; any edge loses. If they then take the corner opposite yours, take one of the two remaining corners.
What if the first player starts on an edge?
Take the centre, a corner touching their mark, or the edge directly opposite. The two edges beside their mark and the two far corners all lose.
How many possible Tic-Tac-Toe games are there?
255,168 different games if you count every move order and stop when someone wins. Rotations and reflections cut that down a lot, and with perfect play every one of the three openings is a draw.
Can the second player win Tic-Tac-Toe?
Only if the first player makes a mistake. The first player can always force at least a draw, and so can the second.