The A Star Is Born co-stars gave an intimate performance, with Cooper serenading Gaga before she sat at the piano to serenade him. As Gaga belted out the last chorus, Cooper came around and settled on the piano bench beside her to finish the song in a passionate pose.
The pair had audiences -- both in the theater and at home -- responding with a standing ovation.
The now Oscar-winning song has been everywhere since its release last fall. It peaked at the fifth spot on the Hot 100 Billboard Chart in October, and the official music video has more than 300 million views on YouTube.
Lady Gaga's journey to the Oscars: 'I couldn't be more proud'
In her emotional acceptance speech for Best Original Song, Gaga thanked Cooper and others and emphasized the importance of hard work.
"If you have a dream, fight for it," she said. "There's a discipline for passion, it's not about how many times you are rejected or you fall down or you're beaten up, it's about how many times you stand up and are brave and you keep on going."
The song was the only win of the night for A Star Is Born, which had eight nominations, including one acting nomination each for Gaga and Cooper.
SEE ALSO: A look at Lady Gaga's memorable red carpet looks
Lady Gaga's most memorable looks from awards season