diff --git a/sqlglot/optimizer/scope.py b/sqlglot/optimizer/scope.py
index 4077964ee5..398a22faac 100644
--- a/sqlglot/optimizer/scope.py
+++ b/sqlglot/optimizer/scope.py
@@ -358,7 +358,7 @@ def references(self) -> t.List[t.Tuple[str, exp.Expression]]:
             for expression in itertools.chain(self.derived_tables, self.udtfs):
                 self._references.append(
                     (
-                        expression.alias,
+                        _get_source_alias(expression),
                         expression if expression.args.get("pivots") else expression.unnest(),
                     )
                 )
@@ -785,7 +785,7 @@ def _traverse_tables(scope):
             # This shouldn't be a problem once qualify_columns runs, as it adds aliases on everything.
             # Until then, this means that only a single, unaliased derived table is allowed (rather,
             # the latest one wins.
-            sources[expression.alias] = child_scope
+            sources[_get_source_alias(expression)] = child_scope
 
         # append the final child_scope yielded
         if child_scope:
@@ -825,7 +825,7 @@ def _traverse_udtfs(scope):
             ):
                 yield child_scope
                 top = child_scope
-                sources[expression.alias] = child_scope
+                sources[_get_source_alias(expression)] = child_scope
 
             scope.subquery_scopes.append(top)
 
@@ -915,3 +915,13 @@ def find_in_scope(expression, expression_types, bfs=True):
         the criteria was found.
     """
     return next(find_all_in_scope(expression, expression_types, bfs=bfs), None)
+
+
+def _get_source_alias(expression):
+    alias_arg = expression.args.get("alias")
+    alias_name = expression.alias
+
+    if not alias_name and isinstance(alias_arg, exp.TableAlias) and len(alias_arg.columns) == 1:
+        alias_name = alias_arg.columns[0].name
+
+    return alias_name
diff --git a/tests/test_optimizer.py b/tests/test_optimizer.py
index 212869a4ff..512358dcab 100644
--- a/tests/test_optimizer.py
+++ b/tests/test_optimizer.py
@@ -871,6 +871,10 @@ def test_scope(self):
         sql = "UPDATE tbl1 SET col = 0"
         self.assertEqual(len(traverse_scope(parse_one(sql))), 0)
 
+        sql = "SELECT * FROM t LEFT JOIN UNNEST(a) AS a1 LEFT JOIN UNNEST(a1.a) AS a2"
+        scope = build_scope(parse_one(sql, read="bigquery"))
+        self.assertEqual(set(scope.selected_sources), {"t", "a1", "a2"})
+
     @patch("sqlglot.optimizer.scope.logger")
     def test_scope_warning(self, logger):
         self.assertEqual(len(traverse_scope(parse_one("WITH q AS (@y) SELECT * FROM q"))), 1)