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It drew just 3.9m viewers or 17% of the audience - though reaction was a little better from Digital Spy readers.
More than 28% of people voting in a forum poll thought the show, set behing the scenes of a TV reality series, was very good.
Another 27%, at the time of writing, rated it good and only 19.9% said it was very poor.
However, BBC One outpaced the newcomer with a 4.1m (18%) audience for Traffic Cops in the 9pm slot.
Rivals' audience was also smaller than openers of ITV1's other recent new dramas, which have been criticised for poor performance. The Palace's debut reached 4.3m, Honest 6m and Moving Wallpaper and Echo Beach both 5m. It trailed last year's slot average by 800,000.
Channel 4 also put up a fight at 9pm with Grand Designs Revisited drawing 3.2m (15%).
On BBC Two Torchwood attracted 2.7m (11.6%) and The Fastest Man On No Legs, for Five, gained 1.1m (4.8%).
> Click here for Digital Spy's video interviews with the cast of Rock Rivals
