4. Add items to the Combat Chain if establishing Attacker and Defender has caused Triggered Abilities to become Pending. 1. The Attacking player, who has Focus, places Triggered Abilities on the Chain first, followed by all non-Defender players in Turn Order, followed by the Defending Player.
§ 464.2.e Core Rules PDF (officieel)
§ 464 Step 1: The Combat Showdown Step
§ 464.2 When Combat opens, it either opens with a Combat Showdown, or the current Showdown becomes a Combat Showdown.