diff -u b/core/lib/Drupal/Core/Routing/PathMatcher.php b/core/lib/Drupal/Core/Routing/PathMatcher.php
--- b/core/lib/Drupal/Core/Routing/PathMatcher.php
+++ b/core/lib/Drupal/Core/Routing/PathMatcher.php
@@ -56,7 +56,21 @@
    */
   public function matchRequestPartial(Request $request) {
 
-    $path = '/' . $request->attributes->get('system_path');
+    // The 'system_path' has language prefix stripped and path alias resolved,
+    // whereas getPathInfo() returns the requested path. In Drupal, the request
+    // always contains a system_path attribute, but this component may get
+    // adopted by non-Drupal projects. Some unit tests also skip initializing
+    // 'system_path'.
+    // @todo Consider abstracting this to a separate object.
+    if ($request->attributes->has('system_path')) {
+      // system_path never has leading or trailing slashes.
+      $path = '/' . $request->attributes->get('system_path');
+    }
+    else {
+      // getPathInfo() always has leading slash, and might or might not have a
+      // trailing slash.
+      $path = rtrim($request->getPathInfo(), '/');
+    }
 
     $parts = array_slice(array_filter(explode('/', $path)), 0, MatcherDumper::MAX_PARTS);
 
diff -u b/core/modules/system/lib/Drupal/system/Tests/Routing/PathMatcherTest.php b/core/modules/system/lib/Drupal/system/Tests/Routing/PathMatcherTest.php
--- b/core/modules/system/lib/Drupal/system/Tests/Routing/PathMatcherTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Routing/PathMatcherTest.php
@@ -88,7 +88,6 @@
     $path = '/path/one';
 
     $request = Request::create($path, 'GET');
-    $request->attributes->set('system_path', trim($path, '/'));
 
     $routes = $matcher->matchRequestPartial($request);
 
@@ -113,7 +112,6 @@
     $path = '/path/1/one';
 
     $request = Request::create($path, 'GET');
-    $request->attributes->set('system_path', trim($path, '/'));
 
     $routes = $matcher->matchRequestPartial($request);
 
@@ -143,7 +141,6 @@
     $path = '/path/1/one/';
 
     $request = Request::create($path, 'GET');
-    $request->attributes->set('system_path', trim($path, '/'));
 
     $routes = $matcher->matchRequestPartial($request);
 
@@ -178,7 +175,6 @@
     $path = '/some/path';
 
     $request = Request::create($path, 'GET');
-    $request->attributes->set('system_path', trim($path, '/'));
 
     try {
       $routes = $matcher->matchRequestPartial($request);
@@ -219,7 +215,6 @@
     $path = '/some/path';
 
     $request = Request::create($path, 'GET');
-    $request->attributes->set('system_path', trim($path, '/'));
 
     try {
       $routes = $matcher->matchRequestPartial($request);
@@ -260,7 +255,6 @@
     $path = '/some/path/here';
 
     $request = Request::create($path, 'GET');
-    $request->attributes->set('system_path', trim($path, '/'));
 
     try {
       $routes = $matcher->matchRequestPartial($request);
@@ -294,7 +288,6 @@
     $path = '/no/such/path';
 
     $request = Request::create($path, 'GET');
-    $request->attributes->set('system_path', trim($path, '/'));
 
     try {
       $routes = $matcher->matchRequestPartial($request);
@@ -308,2 +301,25 @@
 
+  /**
+   * Confirms that system_path attribute overrides request path.
+   */
+  function testSystemPathMatch() {
+    $connection = Database::getConnection();
+    $matcher = new PathMatcher($connection, 'test_routes');
+
+    $this->fixtures->createTables($connection);
+
+    $dumper = new MatcherDumper($connection, 'test_routes');
+    $dumper->addRoutes($this->fixtures->sampleRouteCollection());
+    $dumper->dump();
+
+    $request = Request::create('/path/one', 'GET');
+    $request->attributes->set('system_path', 'path/two');
+
+    $routes = $matcher->matchRequestPartial($request);
+
+    foreach ($routes as $route) {
+      $this->assertEqual($route->getPattern(), '/path/two', 'Found path has correct pattern');
+    }
+  }
+
 }
diff -u b/core/modules/user/lib/Drupal/user/UserRouteController.php b/core/modules/user/lib/Drupal/user/UserRouteController.php
--- b/core/modules/user/lib/Drupal/user/UserRouteController.php
+++ b/core/modules/user/lib/Drupal/user/UserRouteController.php
@@ -7,12 +7,13 @@
 
 namespace Drupal\user;
 
+use Symfony\Component\DependencyInjection\ContainerAware;
 use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
 
 /**
  * Returns responses for User module routes.
  */
-class UserRouteController {
+class UserRouteController extends ContainerAware {
 
   /**
    * Returns the user registration form.