diff --git a/moto/dynamodb2/models.py b/moto/dynamodb2/models.py
index e7277ee6b..4832d7944 100644
--- a/moto/dynamodb2/models.py
+++ b/moto/dynamodb2/models.py
@@ -121,6 +121,14 @@ class Item(object):
                 # TODO deal with other types
                 self.attrs[key] = DynamoType({"S": value})
 
+    def update_with_attribute_updates(self, attribute_updates):
+        for attribute_name, update_action in attribute_updates.items():
+            action = update_action['Action']
+            new_value = update_action['Value'].values()[0]
+            if action == 'PUT':
+                # TODO deal with other types
+                self.attrs[attribute_name] = DynamoType({"S": new_value})
+
 
 class Table(object):
 
@@ -411,12 +419,19 @@ class DynamoDBBackend(BaseBackend):
 
         return table.scan(scan_filters)
 
-    def update_item(self, table_name, key, update_expression):
+    def update_item(self, table_name, key, update_expression, attribute_updates):
         table = self.get_table(table_name)
 
+        if table.hash_key_attr in key:
+            # Sometimes the key is wrapped in a dict with the key name
+            key = key[table.hash_key_attr]
+
         hash_value = DynamoType(key)
         item = table.get_item(hash_value)
-        item.update(update_expression)
+        if update_expression:
+            item.update(update_expression)
+        else:
+            item.update_with_attribute_updates(attribute_updates)
         return item
 
     def delete_item(self, table_name, keys):
diff --git a/moto/dynamodb2/responses.py b/moto/dynamodb2/responses.py
index 57d06bbf3..2be0dda8f 100644
--- a/moto/dynamodb2/responses.py
+++ b/moto/dynamodb2/responses.py
@@ -373,8 +373,9 @@ class DynamoHandler(BaseResponse):
     def update_item(self):
         name = self.body['TableName']
         key = self.body['Key']
-        update_expression = self.body['UpdateExpression']
-        item = dynamodb_backend2.update_item(name, key, update_expression)
+        update_expression = self.body.get('UpdateExpression')
+        attribute_updates = self.body.get('AttributeUpdates')
+        item = dynamodb_backend2.update_item(name, key, update_expression, attribute_updates)
 
         item_dict = item.to_json()
         item_dict['ConsumedCapacityUnits'] = 0.5
diff --git a/tests/test_dynamodb2/test_dynamodb_table_without_range_key.py b/tests/test_dynamodb2/test_dynamodb_table_without_range_key.py
index 808805b8d..6baeb8a12 100644
--- a/tests/test_dynamodb2/test_dynamodb_table_without_range_key.py
+++ b/tests/test_dynamodb2/test_dynamodb_table_without_range_key.py
@@ -122,6 +122,33 @@ def test_item_add_and_describe_and_update():
     })
 
 
+@requires_boto_gte("2.9")
+@mock_dynamodb2
+def test_item_partial_save():
+    table = create_table()
+
+    data = {
+        'forum_name': 'LOLCat Forum',
+        'Body': 'http://url_to_lolcat.gif',
+        'SentBy': 'User A',
+    }
+
+    table.put_item(data=data)
+    returned_item = table.get_item(forum_name="LOLCat Forum")
+
+    returned_item['SentBy'] = 'User B'
+    returned_item.partial_save()
+
+    returned_item = table.get_item(
+        forum_name='LOLCat Forum'
+    )
+    dict(returned_item).should.equal({
+        'forum_name': 'LOLCat Forum',
+        'Body': 'http://url_to_lolcat.gif',
+        'SentBy': 'User B',
+    })
+
+
 @requires_boto_gte("2.9")
 @mock_dynamodb2
 def test_item_put_without_table():