The soulful, 24-year-old musician was overcome with emotion at the conclusion of her moody rendition of The Impressions' People Get Ready.
Crystal later told host Ryan Seacrest her father's presence in the audience during the night of inspirational songs prompted the unexpected crying.
"My dad's here, and this is the first time he's been here," she said.
The show's judges weren't put off by the tears from Crystal, the final contestant to take the stage.
Kara DioGuardi told her that she "just schooled all those contestants". Ellen DeGeneres called Crystal's performance "beautiful," while Randy Jackson offered a standing ovation. Simon Cowell said he was happy to see her so emotional.
"For me, it was in a completely different class than everything we heard tonight," Simon said.
A few finalists were chastised for selecting not-quite-inspirational tunes, including 27-year-old Casey James with Fleetwood Mac's Don't Stop; 17-year-old high school student Aaron Kelly with R. Kelly's I Believe I Can Fly and 26-year-old personal trainer Michael Lynche with Chad Kroeger's Hero. "It felt a little bit artificial," Simon told Michael.
Lee Dewyze was the only other singer to impress the panel. After he crooned Simon And Garfunkel's The Boxer, Randy declared him a "great artist ready to make great music".
Tim Urban and Siobhan Magnus received mixed reactions to their respective renditions of the Goo Goo Dolls' Better Days and Mariah Carey and Whitney Houston's When You Believe. Both were unfazed by the chilly reception. "It's just kind of me," Tim said of his unflappable nature.