As long as you make a payment you've filed for an extension. From the IRS site:
Get an extension when you make a payment
You can also get an extension by paying all or part of your estimated income tax due and indicate that the payment is for an extension using Direct Pay, the Electronic Federal Tax Payment System (EFTPS), or a credit or debit card. This way you won’t have to file a separate extension form and you will receive a confirmation number for your records.
