diff --git a/src/wp-includes/build/pages/font-library/page-wp-admin.php b/src/wp-includes/build/pages/font-library/page-wp-admin.php
index 4d41be02ae892..0ad2dcd3c720f 100644
--- a/src/wp-includes/build/pages/font-library/page-wp-admin.php
+++ b/src/wp-includes/build/pages/font-library/page-wp-admin.php
@@ -153,12 +153,35 @@ function wp_font_library_wp_admin_enqueue_scripts( $hook_suffix ) {
 		// 2. It initializes the boot module as an inline script.
 		wp_register_script( 'font-library-wp-admin-prerequisites', '', $asset['dependencies'], $asset['version'], true );
 
-		// Add inline script to initialize the app using initSinglePage (no menuItems)
+		/*
+		 * Add inline script to initialize the app using initSinglePage (no menuItems).
+		 * The dynamic import is deferred until DOMContentLoaded so that all classic
+		 * script dependencies of @wordpress/boot (wp-private-apis, wp-components,
+		 * wp-theme, etc.) have finished parsing and executing before the boot module
+		 * evaluates. Otherwise, a modulepreloaded @wordpress/boot can win the race
+		 * against the classic-script-printing pass on fast CDN-fronted hosts in
+		 * Chrome, evaluating before wp.theme.privateApis is defined and throwing
+		 * "Cannot unlock an undefined object". See #65103.
+		 */
+		$init_js_function = <<<'JS'
+( mountId, routes ) => {
+	const run = async () => {
+		const mod = await import( "@wordpress/boot" );
+		mod.initSinglePage( { mountId, routes } );
+	};
+	if ( document.readyState === "loading" ) {
+		document.addEventListener( "DOMContentLoaded", run );
+	} else {
+		run();
+	}
+}
+JS;
 		wp_add_inline_script(
 			'font-library-wp-admin-prerequisites',
 			sprintf(
-				'import("@wordpress/boot").then(mod => mod.initSinglePage({mountId: "%s", routes: %s}));',
-				'font-library-wp-admin-app',
+				'( %s )( %s, %s );',
+				$init_js_function,
+				wp_json_encode( 'font-library-wp-admin-app', JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 				wp_json_encode( $routes, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
diff --git a/src/wp-includes/build/pages/font-library/page.php b/src/wp-includes/build/pages/font-library/page.php
index e2849c954ba37..93bb426ae8f84 100644
--- a/src/wp-includes/build/pages/font-library/page.php
+++ b/src/wp-includes/build/pages/font-library/page.php
@@ -159,17 +159,40 @@ function wp_font_library_render_page() {
 		// 2. It initializes the boot module as an inline script.
 		wp_register_script( 'font-library-prerequisites', '', $asset['dependencies'], $asset['version'], true );
 
-		// Add inline script to initialize the app
-		$init_modules = [];
+		/*
+		 * Add inline script to initialize the app.
+		 * The dynamic import is deferred until DOMContentLoaded so that all classic
+		 * script dependencies of @wordpress/boot (wp-private-apis, wp-components,
+		 * wp-theme, etc.) have finished parsing and executing before the boot module
+		 * evaluates. Otherwise, a modulepreloaded @wordpress/boot can win the race
+		 * against the classic-script-printing pass on fast CDN-fronted hosts in
+		 * Chrome, evaluating before wp.theme.privateApis is defined and throwing
+		 * "Cannot unlock an undefined object". See #65103.
+		 */
+		$init_modules     = [];
+		$init_js_function = <<<'JS'
+( mountId, menuItems, routes, initModules, dashboardLink ) => {
+	const run = async () => {
+		const mod = await import( "@wordpress/boot" );
+		mod.init( { mountId, menuItems, routes, initModules, dashboardLink } );
+	};
+	if ( document.readyState === "loading" ) {
+		document.addEventListener( "DOMContentLoaded", run );
+	} else {
+		run();
+	}
+}
+JS;
 		wp_add_inline_script(
 			'font-library-prerequisites',
 			sprintf(
-				'import("@wordpress/boot").then(mod => mod.init({mountId: "%s", menuItems: %s, routes: %s, initModules: %s, dashboardLink: "%s"}));',
-				'font-library-app',
+				'( %s )( %s, %s, %s, %s, %s );',
+				$init_js_function,
+				wp_json_encode( 'font-library-app', JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 				wp_json_encode( $menu_items, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 				wp_json_encode( $routes, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 				wp_json_encode( $init_modules, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
-				esc_url( admin_url( '/' ) )
+				wp_json_encode( admin_url( '/' ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
 
diff --git a/src/wp-includes/build/pages/options-connectors/page-wp-admin.php b/src/wp-includes/build/pages/options-connectors/page-wp-admin.php
index 3f3048b8fb98b..4a9c19cf573a4 100644
--- a/src/wp-includes/build/pages/options-connectors/page-wp-admin.php
+++ b/src/wp-includes/build/pages/options-connectors/page-wp-admin.php
@@ -153,12 +153,35 @@ function wp_options_connectors_wp_admin_enqueue_scripts( $hook_suffix ) {
 		// 2. It initializes the boot module as an inline script.
 		wp_register_script( 'options-connectors-wp-admin-prerequisites', '', $asset['dependencies'], $asset['version'], true );
 
-		// Add inline script to initialize the app using initSinglePage (no menuItems)
+		/*
+		 * Add inline script to initialize the app using initSinglePage (no menuItems).
+		 * The dynamic import is deferred until DOMContentLoaded so that all classic
+		 * script dependencies of @wordpress/boot (wp-private-apis, wp-components,
+		 * wp-theme, etc.) have finished parsing and executing before the boot module
+		 * evaluates. Otherwise, a modulepreloaded @wordpress/boot can win the race
+		 * against the classic-script-printing pass on fast CDN-fronted hosts in
+		 * Chrome, evaluating before wp.theme.privateApis is defined and throwing
+		 * "Cannot unlock an undefined object". See #65103.
+		 */
+		$init_js_function = <<<'JS'
+( mountId, routes ) => {
+	const run = async () => {
+		const mod = await import( "@wordpress/boot" );
+		mod.initSinglePage( { mountId, routes } );
+	};
+	if ( document.readyState === "loading" ) {
+		document.addEventListener( "DOMContentLoaded", run );
+	} else {
+		run();
+	}
+}
+JS;
 		wp_add_inline_script(
 			'options-connectors-wp-admin-prerequisites',
 			sprintf(
-				'import("@wordpress/boot").then(mod => mod.initSinglePage({mountId: "%s", routes: %s}));',
-				'options-connectors-wp-admin-app',
+				'( %s )( %s, %s );',
+				$init_js_function,
+				wp_json_encode( 'options-connectors-wp-admin-app', JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 				wp_json_encode( $routes, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);
diff --git a/src/wp-includes/build/pages/options-connectors/page.php b/src/wp-includes/build/pages/options-connectors/page.php
index 6009dbb2570a9..c5d70c4e41b27 100644
--- a/src/wp-includes/build/pages/options-connectors/page.php
+++ b/src/wp-includes/build/pages/options-connectors/page.php
@@ -159,17 +159,40 @@ function wp_options_connectors_render_page() {
 		// 2. It initializes the boot module as an inline script.
 		wp_register_script( 'options-connectors-prerequisites', '', $asset['dependencies'], $asset['version'], true );
 
-		// Add inline script to initialize the app
-		$init_modules = [];
+		/*
+		 * Add inline script to initialize the app.
+		 * The dynamic import is deferred until DOMContentLoaded so that all classic
+		 * script dependencies of @wordpress/boot (wp-private-apis, wp-components,
+		 * wp-theme, etc.) have finished parsing and executing before the boot module
+		 * evaluates. Otherwise, a modulepreloaded @wordpress/boot can win the race
+		 * against the classic-script-printing pass on fast CDN-fronted hosts in
+		 * Chrome, evaluating before wp.theme.privateApis is defined and throwing
+		 * "Cannot unlock an undefined object". See #65103.
+		 */
+		$init_modules     = [];
+		$init_js_function = <<<'JS'
+( mountId, menuItems, routes, initModules, dashboardLink ) => {
+	const run = async () => {
+		const mod = await import( "@wordpress/boot" );
+		mod.init( { mountId, menuItems, routes, initModules, dashboardLink } );
+	};
+	if ( document.readyState === "loading" ) {
+		document.addEventListener( "DOMContentLoaded", run );
+	} else {
+		run();
+	}
+}
+JS;
 		wp_add_inline_script(
 			'options-connectors-prerequisites',
 			sprintf(
-				'import("@wordpress/boot").then(mod => mod.init({mountId: "%s", menuItems: %s, routes: %s, initModules: %s, dashboardLink: "%s"}));',
-				'options-connectors-app',
+				'( %s )( %s, %s, %s, %s, %s );',
+				$init_js_function,
+				wp_json_encode( 'options-connectors-app', JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 				wp_json_encode( $menu_items, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 				wp_json_encode( $routes, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
 				wp_json_encode( $init_modules, JSON_HEX_TAG | JSON_UNESCAPED_SLASHES ),
-				esc_url( admin_url( '/' ) )
+				wp_json_encode( admin_url( '/' ), JSON_HEX_TAG | JSON_UNESCAPED_SLASHES )
 			)
 		);