It's a bit more complicated than that. You'll have to get a FAA private certificate. One of the requirements for the FAA commercial is to hold a FAA private or be a military pilot. The FAA will issue you a 61.75 private based on your foreign commercial. Than you have to have an instructor sign you off for the writtens. You'll have to be signed off for the checkrides which means you'll have to fly with an instructor to show you're ready for the rides.