The grumpy TV judge called one act "the worst live performance I have ever seen."
The 22-year-old performer sang a stirring rendition of "Bridge Over Troubled Water."
Guest judge Jay Leno pushed the button to vault the young diva to the live show.
The "AGT" judges panel is getting an overhaul next season.
Simon Cowell messed with her at first, but the former "AGT" finalist got a happy ending.
She performed for Simon Cowell for the first time in a decade and aced "Wild Horses."
Osbourne said it was her decision to depart the U.K. version of the show following a controversial Howard Stern interview.
"I was trying to hold it together," the judge said after Michael Ketterer sang James Bay's "Us."
Voodoo, wall-climbing and getting on Mel B's nerves are just part of this act's, er, charm.
"I always said if we could find a dog that could sing, that would be everything to me," Cowell said.
Glennis Grace dazzles with a cover of Houston's "Run to You."
"I'm so glad I pulled it off," Darci Lynne Farmer said.
"I nearly got murdered on live TV."
"I told him he was an arsehole."
"I thought it was quite annoying."