Credit: Michael Becker/Fox

Nobody was certain who would win Fox’s American Idol, but you could easily predict the show’s finale would mark its lowest-rated closer yet.

Given that Idol is down about 29 percent this season, there was no way Wednesday night’s climactic reveal would overtake last May’s finale, which represented the show’s previous finale low.

Last night, Fox says 21.5 million viewers tuned in to watch Phillip Phillips take the top prize, with a 6.3 rating in the adult demographic. That’s down 32 percent from last year, though up 43 percent from last week’s results show.

The Idol slippage this year is significant enough to impact Fox’s overall performance average this season. Later today, Fox is expected to take the ratings crown for the whole season once again, but will have fallen about 9 percent overall for 2011-12 partly due to Idol‘s audience erosion.

Also Wednesday: ABC had some good news. The first season finale of Revenge (7.8 million, 2.4) jumped a hearty 20 percent in the ratings. The finale for new sitcom Don’t Trust the B— (5.7 million, 2.5) jumped 32 percent, though that will come down slightly in the national ratings. Their lead-in, the finale of Modern Family (10 million, 4.0 rating), was up just a tenth.