THE two-hour premiere of “One” – ABC’s heavily promoted rival to “Idol” – was a spectacular bomb.

The show placed fifth in its 9 p.m. timeslot – the lowest-rated reality show debut this summer.

The show was meant to add a “Real World” dimension to the talent show by taking viewers into the house where all the contestants live as cameras follow the kids 24/7.

But its late debut – after talent shows NBC’s “America’s Got Talent,” Fox’s “So You Think You Can Dance” and CBS’s “Rock Star: Supernova” were well under way – probably sank the show.

Even so, the ratings were shockingly low – 3.1 million viewers – dipping below Spanish-language Univision at one point.