EXCLUSIVE: Melissa Rivers Gets Emotional Over Playing Her Late Mom Joan in 'Joy' -- Watch the First Clip!

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Melissa Rivers became overwhelmed with emotion during a sit-down with ET on Tuesday, in which she opened up about the honor of playing her late mother in Joy.

Melissa is the spitting image of her mother Joan Rivers in the movie, not only with her physicality but also vocally. She portrays the legendary comedian during her days hosting on QVC.

WATCH: Melissa Rivers Reveals Where She Scattered Her Mother Joan Rivers' Ashes

"I worked hard on her speech pattern, but not so much the accent because I didn't want it to be an imitation or a caricature," Melissa told ET.

The actress admitted that she teared up when we showed her a clip of her performance.

"I can't watch myself -- especially like that," Melissa said. "I think I was so focused on the details and trying to do a good job that it never hit me that I took this crazy emotional risk until I got home and went, 'What did I just do?'"

WATCH: Melissa Rivers Reveals Why Joan Had a Lifelong Obsession With Death

Joy tells the story of the Mangano family through four generations and details the rise of Joy Mangano (Jennifer Lawrence), who becomes founder and matriarch of a powerful family business dynasty.

"My agent received a phone call, saying, 'David O. Russell wants to meet Melissa,'" Melissa said of joining the movie. "It was all very hush hush and top secret, and I went, 'OK.' In our family when they offer a job, we always joke the answer is, 'Yes, how much?'"

Because this marked her first high-profile film role, Melissa understandably had butterflies as she undertook the task, but she found support in her castmates.

WATCH: Melissa Rivers Describes Joan's Last Moments -- 'I Held Her'

"Everyone was lovely and supportive," Melissa said. "Jen and I talked for a few minutes and she actually quoted back a couple of her favorite jokes of my mom's to me."

Joy, also starring Bradley Cooper and Robert De Niro, opens Christmas Day. Watch the video below to get your first look at Melissa as Joan.