diff --git a/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/FlaskConnexionCodegen.java b/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/FlaskConnexionCodegen.java
index 62fe01e2fb0..7a06ee8b845 100644
--- a/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/FlaskConnexionCodegen.java
+++ b/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/FlaskConnexionCodegen.java
@@ -207,14 +207,16 @@ public class FlaskConnexionCodegen extends DefaultCodegen implements CodegenConf
                 Path path = swagger.getPath(pathname);
                 if(path.getOperations() != null) {
                     for(Map.Entry<HttpMethod, Operation> entry : path.getOperationMap().entrySet()) {
+                        // Normalize `operationId` and add package/class path in front, e.g.
+                        //     controllers.default_controller.add_pet
                         String httpMethod = entry.getKey().name().toLowerCase();
                         Operation operation = entry.getValue();
                         String operationId = getOrGenerateOperationId(operation, pathname, httpMethod);
-                        String xOperationId = underscore(sanitizeName(operationId));
                         if(!operationId.contains(".")) {
-                            operation.setOperationId(controllerPackage + "." + defaultController + "." + xOperationId);
+                            operationId = underscore(sanitizeName(operationId));
+                            operationId = controllerPackage + "." + defaultController + "." + operationId;
                         }
-                        operation.setVendorExtension("x-operationId", xOperationId);
+                        operation.setOperationId(operationId);
                         if(operation.getTags() != null) {
                             List<Map<String, String>> tags = new ArrayList<Map<String, String>>();
                             for(String tag : operation.getTags()) {
@@ -295,4 +297,15 @@ public class FlaskConnexionCodegen extends DefaultCodegen implements CodegenConf
         }
         return super.postProcessSupportingFileData(objs);
     }
+
+    @Override
+    public String toOperationId(String operationId) {
+        operationId = super.toOperationId(operationId);
+        // Use the part after the last dot, e.g.
+        //     controllers.defaultController.addPet => addPet
+        operationId = operationId.replaceAll(".*\\.", "");
+        // Need to underscore it since it has been processed via removeNonNameElementToCamelCase, e.g.
+        //     addPet => add_pet
+        return underscore(operationId);
+    }
 }
\ No newline at end of file
diff --git a/modules/swagger-codegen/src/main/resources/flaskConnexion/controller.mustache b/modules/swagger-codegen/src/main/resources/flaskConnexion/controller.mustache
index cb8544aa1b4..06b3c63fdb0 100644
--- a/modules/swagger-codegen/src/main/resources/flaskConnexion/controller.mustache
+++ b/modules/swagger-codegen/src/main/resources/flaskConnexion/controller.mustache
@@ -3,7 +3,7 @@
 {{#operations}}
 {{#operation}}
 
-def {{vendorExtensions.x-operationId}}({{#allParams}}{{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}}) -> str:
+def {{operationId}}({{#allParams}}{{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}}) -> str:
     return 'do some magic!'
 {{/operation}}
 {{/operations}}
diff --git a/samples/server/petstore/flaskConnexion/swagger/swagger.yaml b/samples/server/petstore/flaskConnexion/swagger/swagger.yaml
index e6455eeab98..1a4ff85e60a 100644
--- a/samples/server/petstore/flaskConnexion/swagger/swagger.yaml
+++ b/samples/server/petstore/flaskConnexion/swagger/swagger.yaml
@@ -47,7 +47,6 @@ paths:
         - "read:pets"
       x-tags:
       - tag: "pet"
-      x-operationId: "add_pet"
     put:
       tags:
       - "pet"
@@ -80,7 +79,6 @@ paths:
         - "read:pets"
       x-tags:
       - tag: "pet"
-      x-operationId: "update_pet"
   /pet/findByStatus:
     get:
       tags:
@@ -116,7 +114,6 @@ paths:
         - "read:pets"
       x-tags:
       - tag: "pet"
-      x-operationId: "find_pets_by_status"
   /pet/findByTags:
     get:
       tags:
@@ -152,7 +149,6 @@ paths:
         - "read:pets"
       x-tags:
       - tag: "pet"
-      x-operationId: "find_pets_by_tags"
   /pet/{petId}:
     get:
       tags:
@@ -187,7 +183,6 @@ paths:
         - "read:pets"
       x-tags:
       - tag: "pet"
-      x-operationId: "get_pet_by_id"
     post:
       tags:
       - "pet"
@@ -224,7 +219,6 @@ paths:
         - "read:pets"
       x-tags:
       - tag: "pet"
-      x-operationId: "update_pet_with_form"
     delete:
       tags:
       - "pet"
@@ -255,7 +249,6 @@ paths:
         - "read:pets"
       x-tags:
       - tag: "pet"
-      x-operationId: "delete_pet"
   /pet/{petId}/uploadImage:
     post:
       tags:
@@ -294,7 +287,6 @@ paths:
         - "read:pets"
       x-tags:
       - tag: "pet"
-      x-operationId: "upload_file"
   /store/inventory:
     get:
       tags:
@@ -318,7 +310,6 @@ paths:
       - api_key: []
       x-tags:
       - tag: "store"
-      x-operationId: "get_inventory"
   /store/order:
     post:
       tags:
@@ -345,7 +336,6 @@ paths:
           description: "Invalid Order"
       x-tags:
       - tag: "store"
-      x-operationId: "place_order"
   /store/order/{orderId}:
     get:
       tags:
@@ -374,7 +364,6 @@ paths:
           description: "Order not found"
       x-tags:
       - tag: "store"
-      x-operationId: "get_order_by_id"
     delete:
       tags:
       - "store"
@@ -398,7 +387,6 @@ paths:
           description: "Order not found"
       x-tags:
       - tag: "store"
-      x-operationId: "delete_order"
   /user:
     post:
       tags:
@@ -421,7 +409,6 @@ paths:
           description: "successful operation"
       x-tags:
       - tag: "user"
-      x-operationId: "create_user"
   /user/createWithArray:
     post:
       tags:
@@ -446,7 +433,6 @@ paths:
           description: "successful operation"
       x-tags:
       - tag: "user"
-      x-operationId: "create_users_with_array_input"
   /user/createWithList:
     post:
       tags:
@@ -471,7 +457,6 @@ paths:
           description: "successful operation"
       x-tags:
       - tag: "user"
-      x-operationId: "create_users_with_list_input"
   /user/login:
     get:
       tags:
@@ -502,7 +487,6 @@ paths:
           description: "Invalid username/password supplied"
       x-tags:
       - tag: "user"
-      x-operationId: "login_user"
   /user/logout:
     get:
       tags:
@@ -519,7 +503,6 @@ paths:
           description: "successful operation"
       x-tags:
       - tag: "user"
-      x-operationId: "logout_user"
   /user/{username}:
     get:
       tags:
@@ -557,7 +540,6 @@ paths:
           description: "User not found"
       x-tags:
       - tag: "user"
-      x-operationId: "get_user_by_name"
     put:
       tags:
       - "user"
@@ -586,7 +568,6 @@ paths:
           description: "User not found"
       x-tags:
       - tag: "user"
-      x-operationId: "update_user"
     delete:
       tags:
       - "user"
@@ -609,7 +590,6 @@ paths:
           description: "User not found"
       x-tags:
       - tag: "user"
-      x-operationId: "delete_user"
 securityDefinitions:
   petstore_auth:
     type: "oauth2"