The former soap star, 35, received a standing ovation and huge cheers from the crowd for his "outstanding" Samba to La Vida Es Un Carnaval with professional Oti Mabuse.
Fletcher bagged 32 points for the routine, with Ballas saying: "It was electrifying. I'm a little bit lost for words. You're coordinated and powerful. To be a great masculine dancer you have to be in touch with your feminine side. You are outstanding."
Motsi said: "Oh my goodness. Kelvin. Are we not happy you stepped in. You have good assets. That hip rotation. That ooziness in your body. That was so rhythmical. That was so fun to watch. I loved it."
Bruno Tonioli joked Fletcher needs to "calm down" saying: "This hunk is on fire! Calm down it's week one. This is the best Samba I have seen on a debut show here in Australia in America."
Even resident Mr Nasty, aka Craig Revel Horwood, bit his acerbic tongue to praise the duo. "Your hands bothered me and your stationary was jagged," he said before adding: "But God works in mysterious ways. Amazing."
Fletcher was thrown into the competition days before the series kicked off after Jamie Laing pulled out after suffering a foot injury. He was in the audience to cheer on the cast of 2019 on Saturday night.
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Strictly Come Dancing is on Saturday, BBC One