Trigger only one collider?

I am making a 2D knights vs goblins type of game. Each characters attack is dealt by a trigger box that is activated when they are attacking. My problem is there are going to be swarms of enemies in the game, and when lets say the player swings his sword, it knocks every one back because the trigger is activated in all of them. What I am trying to get to happen is have the player/weapons trigger only deal damage to one enemy at a time, so the player would only knock back one out of a certain number of enemies, not the whole group. Please note that all the enemies have the same tags, and layers. Also, I am using OnTriggerEnter2D in the enemies controller to know when to take damage and knockback. Any way I can do this easily and efficiently? Thanks!