diff --git a/apps/cli/commands/site/tests/create.e2e.test.ts b/apps/cli/commands/site/tests/create.e2e.test.ts
index 26f2892a3b..402ccd8901 100644
--- a/apps/cli/commands/site/tests/create.e2e.test.ts
+++ b/apps/cli/commands/site/tests/create.e2e.test.ts
@@ -35,7 +35,7 @@ describe.skipIf( ! cliE2ePrerequisitesMet() )( 'CLI e2e: studio site create', ()
 	}, 60_000 );
 
 	it(
-		'creates a site that serves its homepage',
+		'creates a site that serves its homepage and signs in with its admin credentials',
 		{ tags: [ 'e2e' ], timeout: 180_000 },
 		async () => {
 			env = setupCliEnv();
@@ -52,6 +52,10 @@ describe.skipIf( ! cliE2ePrerequisitesMet() )( 'CLI e2e: studio site create', ()
 					sitePath,
 					'--wp',
 					'latest',
+					'--admin-username',
+					'navigator',
+					'--admin-password',
+					'e2e-created-password',
 					'--skip-browser',
 					'--skip-log-details',
 				],
@@ -79,6 +83,18 @@ describe.skipIf( ! cliE2ePrerequisitesMet() )( 'CLI e2e: studio site create', ()
 			} );
 			expect( response.status ).toBe( 200 );
 			expect( response.headers.get( 'content-type' ) ).toMatch( /text\/html/ );
+
+			const signIn = await fetch( `http://localhost:${ String( site.port ) }/wp-login.php`, {
+				method: 'POST',
+				headers: {
+					'content-type': 'application/x-www-form-urlencoded',
+					// wp-login.php rejects the sign-in without WordPress's test cookie.
+					cookie: 'wordpress_test_cookie=WP%20Cookie%20check',
+				},
+				body: new URLSearchParams( { log: 'navigator', pwd: 'e2e-created-password' } ),
+				redirect: 'manual',
+			} );
+			expect( signIn.headers.get( 'set-cookie' ) ).toContain( 'wordpress_logged_in' );
 		}
 	);
 
diff --git a/apps/cli/lib/native-php/site-setup.ts b/apps/cli/lib/native-php/site-setup.ts
index 7a2bed3089..d4c756a141 100644
--- a/apps/cli/lib/native-php/site-setup.ts
+++ b/apps/cli/lib/native-php/site-setup.ts
@@ -169,17 +169,21 @@ function isCoreLanguagePackInstalled( sitePath: string, locale: string ): boolea
 	);
 }
 
+/**
+ * Installs WordPress unless it already is. Returns whether it ran the installer,
+ * which also creates the admin user with the configured credentials.
+ */
 export async function installWordPress(
 	config: ServerConfig,
 	phpVersion: SupportedPHPVersion,
 	signal: AbortSignal,
 	finishInstallPath: string,
 	logToConsole: Logger
-): Promise< void > {
+): Promise< boolean > {
 	const alreadyInstalled = await isWordPressInstalled( config.sitePath, phpVersion, signal );
 	if ( alreadyInstalled ) {
 		logToConsole( `WordPress already installed; skipping installer` );
-		return;
+		return false;
 	}
 
 	const siteTitle = config.siteTitle ?? 'My WordPress Website';
@@ -248,4 +252,5 @@ export async function installWordPress(
 			);
 		}
 	}
+	return true;
 }
diff --git a/apps/cli/php-server-child.ts b/apps/cli/php-server-child.ts
index c46989225c..44bcd79972 100644
--- a/apps/cli/php-server-child.ts
+++ b/apps/cli/php-server-child.ts
@@ -473,6 +473,9 @@ async function startServer( config: ServerConfig, signal: AbortSignal ): Promise
 	// against the imported database would be wrong — and just write Studio's
 	// mu-plugins before starting the workers.
 	const isImportedSite = Boolean( config.autoPrependFile );
+	// Set when this start ran the installer, which created the admin user with the
+	// configured credentials, and no Blueprint ran after it that could change them.
+	let credentialsJustInstalled = false;
 
 	try {
 		stopSignal.throwIfAborted();
@@ -488,12 +491,13 @@ async function startServer( config: ServerConfig, signal: AbortSignal ): Promise
 		stopSignal.throwIfAborted();
 
 		if ( ! isImportedSite ) {
-			await timePhase( 'wordpress_install', () =>
+			const installed = await timePhase( 'wordpress_install', () =>
 				installWordPress( config, phpVersion, stopSignal, FINISH_INSTALL_PATH, logToConsole )
 			);
 			stopSignal.throwIfAborted();
 
 			const blueprint = config.blueprint;
+			credentialsJustInstalled = installed && ! blueprint;
 			if ( blueprint ) {
 				await timePhase( 'blueprint', () =>
 					runBlueprint( config, blueprint, phpVersion, stopSignal )
@@ -543,8 +547,10 @@ async function startServer( config: ServerConfig, signal: AbortSignal ): Promise
 
 		phpProcess = await doStartServer( config, stopSignal );
 		stopSignal.throwIfAborted();
-		await timePhase( 'admin_credentials', () => setAdminCredentials( config, stopSignal ) );
-		stopSignal.throwIfAborted();
+		if ( ! credentialsJustInstalled ) {
+			await timePhase( 'admin_credentials', () => setAdminCredentials( config, stopSignal ) );
+			stopSignal.throwIfAborted();
+		}
 	} catch ( error ) {
 		killPhpProcess();
 		phpProcess = null;