Tamper Proffing server Response

HI experts,

we have two level authentications to our portal Login.

ie. first level --> userid/ password

second leve l --> entering one time password .. that is recievied via sms.

now in the first level when i enter user name and valid pw and on click of login button , the server gives a Response1 (http server response)

now in the second level also when i enter OTP and click button Login , the server gives a Response2 (http server response)

when im logging in for the first time and capture these two responses , and next time if i replace the Response1 with Response2 , then im able to by pass the second level authentication .

Please suggest a solution for the same

Regards

Govardan Raj S