Guy sang his new song, Choir, but some sports fans took to social media to vent their frustrations at his performance and his song of choice.
"And the crowd goes mild," one wrote on Twitter.
"I mean, I've been in emergency department for 10 hours, and it's not the worst part of my day after seeing Guy and the song choice," one said.
Another added: "Never need to head that Guy Sebastian song again."
While some were disgruntled by Guy's performance, others said he "killed it" and they were "delighted" to see him take to the stage.
Following the gig, Guy joined fellow The Voice judge Delta Goodrem, Sony music executive Denis Handlin and his son Pat Handlin, who is engaged to Samantha Jade, in a VIP box.
While they all kicked back together, another celebrity was also watching NSW's 26-20 victory, but from a very different place.
The Project's Tommy Little was shouting for Queensland from a hospital bed in the Gold Coast.
The funnyman, 34, posted a shot of his arm hooked up to a drip alongside an inhaler, but has not said what his mystery illness is.