diff --git a/.changeset/gorgeous-tables-sparkle.md b/.changeset/gorgeous-tables-sparkle.md
new file mode 100644
index 000000000..0613fac56
--- /dev/null
+++ b/.changeset/gorgeous-tables-sparkle.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Simplify nested hydration flow
diff --git a/.github/scripts/bundle-size.mjs b/.github/scripts/bundle-size.mjs
index 618d6e8cb..49c3c5bed 100644
--- a/.github/scripts/bundle-size.mjs
+++ b/.github/scripts/bundle-size.mjs
@@ -23,7 +23,9 @@ export default async function checkBundleSize({ github, context }) {
 		...context.repo,
 		pull_number: PR_NUM,
 	});
-	const clientRuntimeFiles = files.filter(({ filename }) => filename.startsWith(CLIENT_RUNTIME_PATH));
+	const clientRuntimeFiles = files.filter((file) => {
+		return file.filename.startsWith(CLIENT_RUNTIME_PATH) && file.status !== 'removed'
+	});
 	if (clientRuntimeFiles.length === 0) return;
 	
 	const table = [
diff --git a/packages/astro/src/runtime/client/events.ts b/packages/astro/src/runtime/client/events.ts
deleted file mode 100644
index 93a8c2600..000000000
--- a/packages/astro/src/runtime/client/events.ts
+++ /dev/null
@@ -1,20 +0,0 @@
-const HYDRATE_KEY = `astro:hydrate`;
-function debounce<T extends (...args: any[]) => any>(cb: T, wait = 20) {
-	let h = 0;
-	let callable = (...args: any) => {
-		clearTimeout(h);
-		h = setTimeout(() => cb(...args), wait) as unknown as number;
-	};
-	return callable as T;
-}
-
-export const notify = debounce(() => {
-	window.dispatchEvent(new CustomEvent(HYDRATE_KEY));
-});
-
-if (!(window as any)[HYDRATE_KEY]) {
-	if ('MutationObserver' in window) {
-		new MutationObserver(notify).observe(document.body, { subtree: true, childList: true });
-	}
-	(window as any)[HYDRATE_KEY] = true;
-}
diff --git a/packages/astro/src/runtime/client/hydration-directives.d.ts b/packages/astro/src/runtime/client/hydration-directives.d.ts
deleted file mode 100644
index 6832ab24f..000000000
--- a/packages/astro/src/runtime/client/hydration-directives.d.ts
+++ /dev/null
@@ -1,17 +0,0 @@
-import type { GetHydrateCallback, HydrateOptions } from '../../@types/astro';
-
-type DirectiveLoader = (get: GetHydrateCallback, opts: HydrateOptions, root: HTMLElement) => void;
-
-declare global {
-	interface Window {
-		Astro: {
-			idle: DirectiveLoader;
-			load: DirectiveLoader;
-			media: DirectiveLoader;
-			only: DirectiveLoader;
-			visible: DirectiveLoader;
-		};
-	}
-}
-
-export {};
diff --git a/packages/astro/src/runtime/server/astro-island.ts b/packages/astro/src/runtime/server/astro-island.ts
index b24e6c0be..3f93cd817 100644
--- a/packages/astro/src/runtime/server/astro-island.ts
+++ b/packages/astro/src/runtime/server/astro-island.ts
@@ -59,7 +59,6 @@ declare const Astro: {
 					}
 				}
 				async childrenConnectedCallback() {
-					window.addEventListener('astro:hydrate', this.hydrate);
 					let beforeHydrationUrl = this.getAttribute('before-hydration-url');
 					if (beforeHydrationUrl) {
 						await import(beforeHydrationUrl);
@@ -96,17 +95,22 @@ declare const Astro: {
 						this
 					);
 				}
-				hydrate = () => {
-					if (
-						!this.hydrator ||
-						// Make sure the island is mounted on the DOM before hydrating. It could be unmounted
-						// when the parent island hydrates and re-creates this island.
-						!this.isConnected ||
-						// Wait for parent island to hydrate first so we hydrate top-down.
-						this.parentElement?.closest('astro-island[ssr]')
-					) {
+				hydrate = async () => {
+					// The client directive needs to load the hydrator code before it can hydrate
+					if (!this.hydrator) return;
+
+					// Make sure the island is mounted on the DOM before hydrating. It could be unmounted
+					// when the parent island hydrates and re-creates this island.
+					if (!this.isConnected) return;
+
+					// Wait for parent island to hydrate first so we hydrate top-down. The `ssr` attribute
+					// represents that it has not completed hydration yet.
+					const parentSsrIsland = this.parentElement?.closest('astro-island[ssr]');
+					if (parentSsrIsland) {
+						parentSsrIsland.addEventListener('astro:hydrate', this.hydrate, { once: true });
 						return;
 					}
+
 					const slotted = this.querySelectorAll('astro-slot');
 					const slots: Record<string, string> = {};
 					// Always check to see if there are templates.
@@ -126,12 +130,11 @@ declare const Astro: {
 					const props = this.hasAttribute('props')
 						? JSON.parse(this.getAttribute('props')!, reviver)
 						: {};
-					this.hydrator(this)(this.Component, props, slots, {
+					await this.hydrator(this)(this.Component, props, slots, {
 						client: this.getAttribute('client'),
 					});
 					this.removeAttribute('ssr');
-					window.removeEventListener('astro:hydrate', this.hydrate);
-					window.dispatchEvent(new CustomEvent('astro:hydrate'));
+					this.dispatchEvent(new CustomEvent('astro:hydrate'));
 				};
 				attributeChangedCallback() {
 					this.hydrate();