A method of forming and sealing a flexible, reclosable package having a zipper closure and a slider mounted thereon. The reclosable package is initially formed having a pair of opposing side panels and a zipper closure extending between the pair of side panels. The zipper closure is initially attached to the side panels only along a pair of spaced side seals. The reclosable package is filled with product through a fill opening created between the zipper closure and either one of the side panels. Once the package is filled with product, the attachment flanges of the zipper closure are sealed to both of the side panels. Thus, the zipper closure is sealed to the side panels only after product has been inserted into the product package.