The 57-year-old This Morning presenter was supported by husband Eamonn Holmes and son Jack in the audience as the low scores came through.
Ruth and dance partner Anton Du Beke only managed a score of 16 points, joint with Brian Conley and Amy Dowden.
As host Claudia Winkleman announced the voting lines were now open, Anton said: “Would you mind? Only got 16. I was expecting more! I won’t deny.”
Ruth looked at the floor in disappointment and gasped: “Oh no, I’m sorry!”
At the other end of the scoreboard came Aston Merrygold with a total of 31 points – putting him in first place by one.
Bookmakers have now slashed the former JLS star’s odds to win Strictly Come Dancing after he impressed with the last dance of the night.
Coral’s John Hill told Express.co.uk: “Aston was the favourite in the betting going into the opening live show and he has justified that position with a strong performance therefore his odds have been cut once again to lift the Glitterball Trophy.
“Mollie King and Alexandra Burke are clearly strong contenders, however, the surprise package of the night was Debbie McGee who could be the dark horse of the series so her odds have been cut by more than half.
“The betting suggests Brian Conley needs a strong performance next weekend otherwise he will be the first contestant to leave, while Simon Rimmer could also be in the dance off unless he fares better next weekend.”