is guaranteed to win, by simply taking any of the other two corners and then the last, a fork. (since when X takes the third corner, O can only take the position between the two Xs. Then X can take the only remaining corner to win) If O responds with an edge mark, X is guaranteed to win, by taking center, then O can only take the corner opposite the corner which X plays first. Finally, X can take a corner to create a fork, and then X will win on the next move. Further details Consider a board with the nine positions numbered as follows: When X plays 1 as their opening move, then O should take 5. Then X takes 9 (in this situation, O should not take 3 or 7, O should take 2, 4, 6 or 8): X1 → O5 → X9 → O2 → X8 → O7 → X3 → O6 → X4, this game will be a draw. or 6 (in this situation, O should not take 4 or 7, O should take 2, 3, 8 or 9. In fact, taking 9 is the best move, since a non-perfect player X may take 4, then O can take 7 to win). X1 → O5 → X6 → O2 → X8, then O should not take 3, or X can take 7 to win, and O should not take 4, or X can take 9 to win, O should take 7 or 9. X1 → O5 → X6 → O2 → X8 → O7 → X3 → O9 → X4, this game will be a draw. X1 → O5 → X6 → O2 → X8 → O9 → X4 (7) → O7 (4) → X3, this game will be a draw. X1 → O5 → X6 → O3 → X7 → O4 → X8 (9) → O9 (8) → X2, this game will be a draw. X1 → O5 → X6 → O8 → X2 → O3 → X7 → O4 → X9, this game will be a draw. X1 → O5 → X6 → O9, then X should not take 4, or O can take 7 to win, X should take 2, 3, 7 or 8. X1 → O5 → X6 → O9 → X2 → O3 → X7 → O4 → X8, this game will be a draw. X1 → O5 → X6