"I honestly couldn't be any more happy while watching @selenagomez deliver that performance," the DJ wrote on Twitter Monday. "Her talent is unreal, blessed to call her my friend."
Before the show, Marshmello also let Billboard know that Gomez was his favorite singer to work with.
While Marshmello was impressed by Gomez's performance of "Wolves," some members of the audience at home were not. Plenty of fans thought she was lip-synching.
Another added, "If only she didn't lip sync, it would've been a great performance."
Then again, many of Gomez's fans pointed out that it was the 25-year-old's first time on stage since she had a life-saving kidney transplant in September. It was also her first live performance in over a year.
"I'm disappointed. Not [because] of Selena Gomez. [Because] of some people. She did an amazing job even though she lip synced. She had such a rough time and had a kidney transplantation & could have died. She looked so sad at the end bc she knew it wasn't her best performance," one fan wrote.
"Wolves" is Gomez's third single of 2017, following "Fetish" and "Bad Liar."