"Killshot" - Eminem's response to MGK's "Rap Devil", garnered a staggering 38.1 million views in its first 24 hours, making it the biggest hip-hop debut ever.
Meanwhile, reports suggesting Kelly was booed during a Sunday night performance of his Slim Shady diss track on the Fall Out Boy tour have emerged, with one fan claiming fans at the concert sneered at the rapper as he took aim at Eminem.
Kelly posted a shot from the gig on social media - in it he stands facing the camera with his back to the audience, wearing a T-shirt emblazoned with the "Killshot" cover featuring his face as a target practice sign, and flipping the middle finger as fans behind him do the same.
But now it seems the crowd may have been flipping him off - not Eminem.
"MGK took this photo in front of the Fall Out Boy audience that was waiting for them to come on stage and do their set," one Twitter user writes beneath the photo. "He was wearing a jacket when he asked the crowd if they would put up their middle fingers for a picture, he turned around to take the jacket off and they had no idea what shirt he was wearing.
"He couldn't pull a crowd this big, of course they were excited, they were waiting to see the band that they actually paid for!"
Another Eminem devotee adds: "Your s**tty rapper was at a fall out boys concert, making everyone take a picture with him without anyone knowing what for or even the shirt he was wearing. As soon as they saw his shirt his a** got boo'd off stage AND HE STILL POSTED THIS PHONY A** PHOTO."
A third fan tweets: "We all know what actually happened on that stage... right?"
Machine Gun Kelly claimed his photo showed how much support he has in his ongoing war of words with Eminem.
It received more than 600,000 likes.