Magento – Magento 2.2.5: Overriding Admin Controller sales/order

I need to override Admin sales/order/index controller, but still getting 404. Below the Steps I take to override –

Created My Custom Module
app/code/A2bizz/Order/registration.php

<?php
\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'A2bizz_Order',
    __DIR__
);

app/code/A2bizz/Order/etc/module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="A2bizz_Order" setup_version="2.0.0" schema_version="2.0.0">
        <sequence>
            <module name="Magento_Sales"/>
            <module name="Magento_Rule"/>
            <module name="Magento_Catalog"/>
            <module name="Magento_Customer"/>
            <module name="Magento_Payment"/>
            <module name="Magento_SalesSequence"/>
        </sequence>
    </module>
</config>

app/code/A2bizz/Order/Controller/Adminhtml/Order/Index.php

<?php

    namespace A2bizz\Order\Controller\Adminhtml\Order;

    class Index extends \Magento\Sales\Controller\Adminhtml\Order\Index
    {
        public function execute()
        {
            $this->messageManager->addSuccess('Message from new admin controller.');
            // Do your stuff here
            return parent::execute();
        }
    }

app/code/A2bizz/Order/etc/adminhtml/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\Sales\Controller\Adminhtml\Order\Index" 
                type="A2bizz\Order\Controller\Adminhtml\Order\Index" />
</config>

if anyone can help me on what I am doing wrong.
Thanks