diff --git a/moto/dynamodb2/models.py b/moto/dynamodb2/models.py
index 7525a43a9..7590ee1e1 100644
--- a/moto/dynamodb2/models.py
+++ b/moto/dynamodb2/models.py
@@ -3,6 +3,7 @@ from collections import defaultdict
 import datetime
 import decimal
 import json
+import re
 
 from moto.compat import OrderedDict
 from moto.core import BaseBackend, BaseModel
@@ -115,28 +116,31 @@ class Item(BaseModel):
         }
 
     def update(self, update_expression, expression_attribute_names, expression_attribute_values):
-        ACTION_VALUES = ['SET', 'set', 'REMOVE', 'remove']
-
-        action = None
-        for value in update_expression.split():
-            if value in ACTION_VALUES:
-                # An action
-                action = value
-                continue
-            else:
+        # Update subexpressions are identifiable by the operator keyword, so split on that and
+        # get rid of the empty leading string.
+        parts = [p for p in re.split(r'\b(SET|REMOVE|ADD|DELETE)\b', update_expression) if p]
+        # make sure that we correctly found only operator/value pairs
+        assert len(parts) % 2 == 0, "Mismatched operators and values in update expression: '{}'".format(update_expression)
+        for action, valstr in zip(parts[:-1:2], parts[1::2]):
+            values = valstr.split(',')
+            for value in values:
                 # A Real value
-                value = value.lstrip(":").rstrip(",")
-            for k, v in expression_attribute_names.items():
-                value = value.replace(k, v)
-            if action == "REMOVE" or action == 'remove':
-                self.attrs.pop(value, None)
-            elif action == 'SET' or action == 'set':
-                key, value = value.split("=")
-                if value in expression_attribute_values:
-                    self.attrs[key] = DynamoType(
-                        expression_attribute_values[value])
+                value = value.lstrip(":").rstrip(",").strip()
+                for k, v in expression_attribute_names.items():
+                    value = re.sub(r'{0}\b'.format(k), v, value)
+
+                if action == "REMOVE":
+                    self.attrs.pop(value, None)
+                elif action == 'SET':
+                    key, value = value.split("=")
+                    key = key.strip()
+                    value = value.strip()
+                    if value in expression_attribute_values:
+                        self.attrs[key] = DynamoType(expression_attribute_values[value])
+                    else:
+                        self.attrs[key] = DynamoType({"S": value})
                 else:
-                    self.attrs[key] = DynamoType({"S": value})
+                    raise NotImplementedError('{} update action not yet supported'.format(action))
 
     def update_with_attribute_updates(self, attribute_updates):
         for attribute_name, update_action in attribute_updates.items():
@@ -345,7 +349,6 @@ class Table(BaseModel):
     def query(self, hash_key, range_comparison, range_objs, limit,
               exclusive_start_key, scan_index_forward, index_name=None, **filter_kwargs):
         results = []
-
         if index_name:
             all_indexes = (self.global_indexes or []) + (self.indexes or [])
             indexes_by_name = dict((i['IndexName'], i) for i in all_indexes)
diff --git a/moto/dynamodb2/responses.py b/moto/dynamodb2/responses.py
index 1d9b70043..bf24e9964 100644
--- a/moto/dynamodb2/responses.py
+++ b/moto/dynamodb2/responses.py
@@ -316,24 +316,26 @@ class DynamoHandler(BaseResponse):
             else:
                 index = table.schema
 
-            key_map = [column for _, column in sorted(
-                (k, v) for k, v in self.body['ExpressionAttributeNames'].items())]
+            reverse_attribute_lookup = dict((v, k) for k, v in
+                                            six.iteritems(self.body['ExpressionAttributeNames']))
 
             if " AND " in key_condition_expression:
                 expressions = key_condition_expression.split(" AND ", 1)
 
-                index_hash_key = [
-                    key for key in index if key['KeyType'] == 'HASH'][0]
-                hash_key_index_in_key_map = key_map.index(
-                    index_hash_key['AttributeName'])
+                index_hash_key = [key for key in index if key['KeyType'] == 'HASH'][0]
+                hash_key_var = reverse_attribute_lookup.get(index_hash_key['AttributeName'],
+                                                            index_hash_key['AttributeName'])
+                hash_key_regex = r'(^|[\s(]){0}\b'.format(hash_key_var)
+                i, hash_key_expression = next((i, e) for i, e in enumerate(expressions)
+                                              if re.search(hash_key_regex, e))
+                hash_key_expression = hash_key_expression.strip('()')
+                expressions.pop(i)
 
-                hash_key_expression = expressions.pop(
-                    hash_key_index_in_key_map).strip('()')
-                # TODO implement more than one range expression and OR
-                # operators
+                # TODO implement more than one range expression and OR operators
                 range_key_expression = expressions[0].strip('()')
                 range_key_expression_components = range_key_expression.split()
                 range_comparison = range_key_expression_components[1]
+
                 if 'AND' in range_key_expression:
                     range_comparison = 'BETWEEN'
                     range_values = [