diff --git a/src/Symfony/Component/DependencyInjection/Container.php b/src/Symfony/Component/DependencyInjection/Container.php
index ab0abf316f..40e171b3d8 100644
--- a/src/Symfony/Component/DependencyInjection/Container.php
+++ b/src/Symfony/Component/DependencyInjection/Container.php
@@ -240,8 +240,9 @@ class Container implements IntrospectableContainerInterface
     {
         $id = strtolower($id);
 
-        return array_key_exists($id, $this->services)
-            || array_key_exists($id, $this->aliases)
+        return isset($this->services[$id])
+            || array_key_exists($id, $this->services)
+            || isset($this->aliases[$id])
             || method_exists($this, 'get'.strtr($id, array('_' => '', '.' => '_')).'Service')
         ;
     }
@@ -267,16 +268,21 @@ class Container implements IntrospectableContainerInterface
      */
     public function get($id, $invalidBehavior = self::EXCEPTION_ON_INVALID_REFERENCE)
     {
-        $id = strtolower($id);
-
-        // resolve aliases
-        if (isset($this->aliases[$id])) {
-            $id = $this->aliases[$id];
-        }
-
-        // re-use shared service instance if it exists
-        if (array_key_exists($id, $this->services)) {
-            return $this->services[$id];
+        // Attempt to retrieve the service by checking first aliases then
+        // available services. Service IDs are case insensitive, however since
+        // this method can be called thousands of times during a request, avoid
+        // calling strotolower() unless necessary.
+        foreach (array(false, true) as $strtolower) {
+            if ($strtolower) {
+                $id = strtolower($id);
+            }
+            if (isset($this->aliases[$id])) {
+                $id = $this->aliases[$id];
+            }
+            // Re-use shared service instance if it exists.
+            if (isset($this->services[$id]) || array_key_exists($id, $this->services)) {
+                return $this->services[$id];
+            }
         }
 
         if (isset($this->loading[$id])) {
@@ -339,7 +345,8 @@ class Container implements IntrospectableContainerInterface
      */
     public function initialized($id)
     {
-        return array_key_exists(strtolower($id), $this->services);
+        $id = strtolower($id);
+        return isset($this->services[$id]) || array_key_exists($id, $this->services);
     }
 
     /**