A method for fabricating a fitmented flexible bottle is disclosed which involves feeding webs including one or more gussets, creating perimeter seals around only the top portion of the bottle, inserting the fitment from the input end of the machine in the direction of web travel, forming the remainder of the perimeter seams, detaching the nascent bottle from the web, and sealing the neck section of the bottle to the fitment by clamping the neck section with a heated clamp, and preferably repeating the seal operation at a different radial angle. Sealing the fitment by application of ultrasonic energy is also disclosed. In another embodiment, the fitment is sealed to the neck section of the bottle by utilizing heated wheels against the neck and rotating the bottle to create a seal all around the neck.