So far at least, “American Inventor” is looking like a good idea for ABC.

The two-hour Thursday preem of the skein from “American Idol’s” Simon Cowell won its timeslot in key demo categories, lifting the Alphabet to victory over CBS’ coverage of the NCAA men’s basketball tourney and regular lineups on the other nets.

According to Nielsen, the unscripted search for the next great invention averaged a 5.4 rating/15 share in adults 18-49 and 14.15 million viewers from 8 to 10 — the net’s strongest demo delivery with series in the time period since November 2000. Show grew with each half-hour, peaking at 9:30 with a 6.2/16 in 18-49.

Combined with “Primetime” at 10 (3.2/9 in 18-49, 8.4 million viewers overall), ABC logged its first in-season Thursday 18-49 victory with series programming in at least 15 years.

“Inventor” benefited from a smart sked move that allowed it to premiere one week after Fox’s dominant “American Idol” had ended its special three-week Thursday run and at a time when CBS’ regular tandem of “Survivor” and “CSI” was on the bench due to college hoops. The Eye duo will also be off the night this week.

For the next four Thursdays, ABC figures to score with special editions of Sunday hit “Extreme Makeover: Home Edition” (featuring families in the Gulf Coast area affected by Hurricane Katrina) leading into “Inventor” in its regular 9 o’clock slot. Earlier this year, the Alphabet established itself as a Thursday player with another unscripted skein, “Dancing With the Stars.”

ABC’s success on the night affected NBC’s comedy block, with “Four Kings” drooping at 8:30 (2.9/8 in 18-49, 6.82m) and losing 3 share points from its “Will & Grace” lead-in (3.6/11, 9.09m). That led into the lowest-rated firstrun seg to date for “My Name Is Earl” (4.5/12, 10.59m).

“The Office” again held onto most of its “Earl” lead-in at 9:30 (4.2/11, 8.85m), while “ER” was on the low end despite easily winning the 10 o’clock hour (5.8/15, 13.98m).

Fox was lackluster with the series premiere of “The Loop” (2.0/6 in 18-49, 4.75m), which ran fourth at 8:30 despite a big sampling opportunity the night before with a special preview seg behind “American Idol.”

As for the NCAA tourney, CBS ran third Thursday in 18-49 but first in key male demos. Net reports that the preliminary national household rating average for the full-day first-round action on Thursday and Friday (5.0/12) was up 4% from last year’s 4.8/11 and the best since 1997 (5.2/13). Second-round action aired Saturday and Sunday on the net.