The diva from Romford, Essex closed the show with rival Mo as they belted out the Sam Cooke classic A Change is Gonna Come.
While Diamond was the clear favourite with the viewers at home, Jennifer, 35, made a shock decision to boot her out of the contest.
Though, in a matter of seconds, Gavin slammed his shiny white button and put the soul queen back in the race, which suited her perfectly.
After breaking down in excitement, Diamond shrieked: “I was so happy because I was originally going to go with Gavin but Jennifer stole it.”
In turn, viewers praised the Bush frontman and his new team member in their droves on Twitter.
“YESSS!!!! @GavinRossdale!!!! Thank you for keeping Diamond in the show. What an outstanding voice to listen to,” beamed one fan, as another agreed: “I’m so glad @GavinRossdale stole Diamond! It would have been horribly unfair if she’d had to leave. She’s awesome!”
A third cried: “Great steal for #TeamGavin as Diamond also has a fantastic voice.”
One more enthused: “Gavin Rossdale! In love with you right now, you definitely needed Diamond in your team,” before someone else wrote: “I knew Mo and Diamond would both go through. That battle was so close.”
What’s more, the audience appeared to have taken a U-turn on the 51-year-old coach, after initially asking “who is Gavin Rossdale?” they’ve now tipped him to win.
“Gavin’s a dark horse, he’s been excellent tonight in song choices. He’ll do well with Diamond,” teased one fan.
However, some of his other choices didn’t get the same response as many felt the rocker should have picked Millicent Weaver over Max Vickers.
The Voice UK continues tomorrow night at 7pm on ITV.