Fox reality hit “American Idol” had a strong but hardly spectacular penultimate episode last night, falling significantly from the same time last year.

“Idol” averaged a 9.3 adults 18-49 rating, according to Nielsen overnights, one of its lowest ratings of the year and off 24 percent from a 12.3 on the same night last year. It pulled 24.5 million total viewers, down 23 percent from 31.8 million on the same night last year.

“Idol” still dominated primetime, lifting Fox to victory on the second-to-last night of sweeps. But it showed once again that “Idol” lost a lot of steam in the second half of the season, after outpacing last year during the first half. Other hit shows have seen similar ratings declines this spring.

That also led to a somewhat disappointing debut for the new Fox summer reality series “On the Lot,” which the network smartly premiered at 9 p.m. last night after “Idol.” The Steven Spielberg-produced show, about wannabe filmmakers, averaged a 4.1 adults 18-49 rating, retaining only 44 percent of its lead-in. Among total viewers it drew almost 9 million, holding a mere 37 percent of “Idol’s” audience.

It fell 36 percent from its first half hour to its second, from a 5.0 to a 3.2. But “Lot” had the difficult task of facing the first hour of the fourth-season finale of ABC’s hit “Dancing with the Stars.”

The two-hour show averaged a 6.6 in adults 18-49 and 22.7 million total viewers. Its numbers were down 7 percent and 17 percent, respectively, from last fall’s season three finale, won by ex-Dallas Cowboys great Emmitt Smith.

Last fall’s finale was only one hour. The final hour last night averaged a 6.9, nearly the same as last fall’s 7.1.

Meanwhile, Fox finished first for the night among viewers 18-49 with a 6.7 average rating and an 18 share, followed by ABC at 5.3/14. CBS was third at 2.8/7, NBC fourth at 2.7/7, Univision fifth at 2.1/6 and CW sixth at 0.8/2.
 
At 8 p.m. Fox led with a 9.3 for “American Idol,” with CBS second with a 3.3 for “NCIS.” ABC was third that hour with a 2.7 for “The Bachelor: After the Final Rose,” Univision fourth with a 2.0 for “La Fea Mas Bella,” NBC fifth with a 1.6 for “Dateline” and CW sixth with a 0.8 for its first hour of the series finale of “Veronica Mars.”
 
ABC took the lead at 9 p.m. with a 6.3 for the first hour of the “Stars” results show, while Fox slipped to second with a 4.1 for “Lot.” CBS was third with a 2.5 for the first hour of the movie “Jesse Stone: Sea Change” and Univision and NBC tied for fourth at 2.3, Univision for “Destilando Amor” and NBC for a repeat of “Law & Order: Criminal Intent.” That left CW sixth with a 0.9 for the second half of “Veronica Mars.”
 
At 10 p.m. ABC led again, this time with a 6.9 for the second half of “Stars.” NBC moved to second with a 4.1 for “Law & Order: Special Victims Unit,” with CBS third with a 2.4 for the second half of its movie and Univision fourth with a 2.0 for “Nuestra Belleza Latina.”
 
Among households, ABC led the night with an 11.8 average rating and a 19 share, with Fox second at 9.9/16, CBS third at 8.5/13, NBC fourth at 5.2/8, Univision fifth at 2.4/4 and CW sixth at 1.3/2.