The 3-year-old wowed the audience when he launched into the routine at New York's Madison Square Garden.
While the Spices sang hit single Mama, Cruz started spinning on his head.
'A minute into the song, Cruz [began] moving a little to the music and then all of a sudden started breakdancing…and he was awesome at it,' an onlooker tells Perez Hilton.
'All the girls had to stop singing cuz they were laughing so hard… He did a little head stand, then even spun on his head a little.
'They couldn't get him off the stage when the song was over. It was the most adorable thing I've ever seen!'
Mum Victoria, 33, couldn't be prouder.
'We've been upstaged,' she told fans. 'He's the next Justin Timberlake.'
Perhaps Cruz could go into show business with his brothers – Brooklyn, 8, and Romeo, 5 - as the Beckham Three.
Geri Halliwell's daughter Bluebell, 1, also shone as she joined in with singing Mama.
Ginger, 35, said it made the New York trip perfect.
'Victoria's son Cruz was a little star,' she writes on the official Spice Girls site. 'We all had our children up on stage tonight and Cruz started break dancing! How cool is that? It's clearly in the family.
'I love New York so much and I have had a blast here. I hit the ground running… enjoying the nightlife, the vintage shopping, the food and the people.'
See the video of Cruz breakdancing...
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