Simon Cowell, who initially urged Jonathan to continue alone during their first audition, admitted that he was wrong to doubt their ability as a duo.
Cowell said: "There is a lot at stake here and, like I said during the first audition, Charlotte, I believed that you were holding him back. And you made the decision to stay together, Jonathan. And that was the best decision you ever made."
The Syco boss added that the performance was "genuinely" among his "favourite ever Britain's Got Talent performances".
Amanda Holden, who was absent at the recording of the pair's original audition, echoed Cowell's sentiment later in the show.
Alesha Dixon said: "There was a lot of pressure on you tonight. Let me tell you, you held your own. You started that song so beautifully. This is a special friendship and a special chemistry between you. And when you sang, Jonathan, I felt that through every part of my body. That was incredible."
Both Jonathan and Charlotte were speechless when Ant and Dec spoke to them following the panel's verdict.
The duo later made it through to Britain's Got Talent's final on Saturday (May 12) after coming top of the viewers' vote.