"It's hard to take your eyes off her," Smith, 20, tells PEOPLE. "Even in a scene, its hard to stay focus just because she's magnetic to watch."
Seventeen years have passed since the Buffy the Vampire Slayer alum stepped into the shoes of the scheming society girl, and Gellar, 39, even dyed her blonde hair brunette to get back into character.
"She really took care of me," says Smith, a relative newcomer who can next be seen in Wolves alongside Michael Shannon. "She was very adamant about doing what was necessary in order to make the scene come to life or to make your choices true."
NBC's follow-up to the 1999 movie follows Bash Casey (Smith), the son of Sebastian Valmont (portrayed by Ryan Phillippe in the movie) and Annette Hargrove (Reese Witherspoon in the movie and Kate Levering in the series). After Bash unearths his deceased father's journal where he chronicled all of his misdeeds, he takes his father's 1957 Jaguar Roadster from Kansas to San Francisco, where he meets his aunt Kathryn (Gellar), who is fighting for control of Valmont International and him.
"It's like his mom on one shoulder – she's the angel – and then there's Kathryn on the other side like the devil," Smith teases. "They're both kind of pulling for me. Will I become the person my mom raised me to be or am I destined to become like my father and go down that road of power and prestige?"
"It was overwhelming in a sense," the Virginia-to-California transplant actor says. "For my character Bash, that's his first time experiencing anything of that value, that huge next, next level world.It was nice I didn't have any preconceived ideas about that lifestyle either. I could kind of be in shock and awe like he's in shock and awe."
Peter Gallagher, Coby Bell and Samantha Logan also star in the series, which finished filming April 1 in San Francisco.