This one plagued me for days until I finally tracked it down. The song is called "He Needs Me", written by Harry Nilsson, and sung by Shelley Duvall, approx 1980. It was in Punch Drunk Love and also in Popeye. It's easily available as an mp3. Those who can't get it out of their head are not alone. The eye-candy in the Nike Tennis advert/commercial (showing here in NZ on TV) probably helps form a mental link best left unexplored if the comments from other websites are any indication.