How to Defend in Gomoku: Stop the Four, Block the Double-Three
Defense wins as many Gomoku games as attack. Learn to spot open threes and fours, decide whether to block or extend, and avoid the passive defending that loses games.
New players lose most of their games by reacting one move too late: they defend the open three, but only after it already became a four. Good defense is about seeing threats one move earlier and knowing when blocking is the wrong move. This is the fastest skill to improve your win rate.
The threat hierarchy you must know
- Five: the game is over.
- Open four (活四): already unstoppable — two winning points, your opponent can only pick one.
- Four (冲四): must be blocked immediately; one move of delay and it is a five.
- Open three (活三): the real danger. An open three becomes an open four next move, which is game over. Block it the moment it appears.
- Broken three (眠三): a sleeping threat. Not urgent by itself, but never give your opponent two of them at once.
When to block vs when to extend
The classic beginner mistake is defending every single move. If your opponent makes a weak move that creates no threat, use that turn to extend your own attack instead — a move that builds your own open three is worth more than a block that gains nothing.
Only block when the opponent has an immediate threat (an open three, a four, or a move that creates two threats at once). Everything else is a chance to counterattack.
The double-three trap
The most common winning pattern is a move that creates two open threes (or an open three and a four) at once. You can only block one of them — next turn the other one wins. Whenever the board has room for this, assume your opponent is aiming at it and play a move that prevents both threats from forming.
A simple defense checklist
- Scan for open threes first — they are the seeds of every loss.
- Count open ends: a three with both ends open is twice as dangerous.
- Block the side that gives your opponent more space, not the closer side.
- If you must choose between blocking and making your own open three, make your own open three.
FAQ
How do I stop an open four?
You cannot. An open four has two winning points, so it is already a forced win. The only defense is not letting the opponent create one — which means blocking open threes early.
Should I always block the open three?
Yes. If there is an open three on the board, it is almost always correct to block it immediately. The only exception is when you already have a forced win of your own.
Why do I keep losing even though I defend every move?
Because passive defense hands the initiative to your opponent. Every move where you block without creating a threat of your own lets them build a new attack. Defense must be combined with counterattack.
A simple defense checklist
- Scan for open threes first
They are the seed of every loss. Find them before they become fours.
- Count open ends
A three with both ends open is twice as dangerous as one with a single end.
- Block the side with more space
Prefer to block the end that gives your opponent more room to extend.
- Counterattack, don’t just block
When there is no immediate threat, use your turn to build your own open three instead of defending.