If Fox’s “My Big Fat Obnoxious Fiancé” is going to help pull Fox out of the doldrums, it’s going to have to do it without an “American Idol” lead-in. But even with “Idol” to boost it in its debut, “Fiancé” bled enough audience that Fox should be concerned.
   As expected, the third-season premiere of “American Idol” lifted Fox to a dominating Monday night, but the second half of the new show “My Big Fat Obnoxious Fiancé” showed alarming viewer leakage.
  Mondays have been a disaster for Fox since the fall, when “Joe Millionaire 2” and “Skin” bombed. Thus far this season Fox is in third place among adults 18-49.
   “Idol” drew 29 million viewers at 8 p.m., 2.5 million more than last year’s premiere and the biggest premiere for any show this season, according to Nielsen overnights.
   Final numbers, due out later today, could be even better, as “Idol” actually ran about eight minutes over into the 9 p.m. “Fiancé.”
   But even with those extra eight minutes, “Fiancé” lost more than a third of “Idol’s” lead-in, averaging 19.6 million viewers.
   Among the show’s target adults 18-49 audience the slip wasn’t as severe. “American Idol” averaged a 12.5 from 8 to 9 p.m., one of the highest ratings this season for any non-sporting event. The show grew 15 percent from start to finish, and gave “Fiancé” a 13.4 rating heading into the 9 p.m. hour.
   But “Fiancé” fumbled away 20 percent of that audience in the first half-hour, dipping to a 10.8. In the second half-hour 18 percent of the audience fled.
  Media people won’t be surprised by this. 
  In a poll of Media Life readers last week, nearly 70 percent predicted that “Fiancé” would be a big fat flop while 31.5 percent predicted a hit.
   Media Life TV critic A.J. Livsey worried that people wouldn't get "Fiancé's" irony: "While it's something most viewers are likely to miss altogether, it is the show's clever manipulation of irony that makes 'Fiancé' palatable and even enjoyable."
   The bad news for Fox is that starting next week, “Fiancé” won’t have “Idol” to provide a ratings buoy.
    The good news is that, almost two weeks after its supposed season finale, midseason hit “The Simple Life” will return with one extra hour-long episode this Monday.
   That should provide at least a small boost to “Fiancé,” but anything over a 5.5 adults 18-49 rating would be a terrific performance for the show. Fox still has not decided how to plug the 8 p.m. hole, and will likely make its decision depending on how “Fiancé” does its first few episodes apart from “Idol.”