Masterson's first film appearance was in The Stepford Wives (1975) at the age of eight, playing a daughter to her real-life father. Rather than continue her career as a child actor, she chose to continue her studies, although she did appear in several productions at the Dalton School. In 1985, she returned to cinema in Heaven Help Us as Danni, a courageous teen running the soda shop of her gravely depressed Dad. She appeared with Sean Penn and Christopher Walken in the film At Close Range (1986) as Brad Jr's girlfriend Terry, a film based on an actual rural Pennsylvania crime family led by Bruce Johnston, Sr. during the 1960s and 1970s. She later starred as the tomboyish drumming Watts in the teenage drama Some Kind of Wonderful (1987). As a result, she is loosely connected with the Brat Pack. The same year Francis Ford Coppola cast her in Gardens of Stone in which she acted with her parents, hired by Coppola to play her on-screen parents. In 1989, she played in Chances Are alongside Cybill Shepherd, Ryan O'Neal and Robert Downey Jr., and she starred as Lucy Moore, a teenage girl giving up her first baby to a wealthy couple, played by Glenn Close and James Woods in Immediate Family. For her work in that film she received a "Best Supporting Actress" award from the National Board of Review of Motion Pictures.