"Little did I know I would be relying on my faith, especially as much as I did this past week," Osmond told the audience at her Las Vegas show on Tuesday.
The singer's emotional return to the Flamingo Hotel & Casino stage comes less than two weeks after her son's death and just one day after his funeral.
"I just think that we need to give a big round of applause to my sister for even coming onstage tonight," brother Donny Osmond said after their opening number.
During the show, Osmond, standing in front of a starry backdrop, wore a robe of white feathers and dedicated a song to her 18-year-old son, Michael Blosil, whom she referred to as "my angel."
Marie Osmond's son dies
"God bless you all," she said. "The way Osmonds survive is we keep singing and that's what we want to do tonight. I know my son would want that."
Blosil died on Feb. 26 after falling from a balcony in Los Angeles. Toxicology tests are pending to determine if alcohol or drugs played a factor in his death.