The first part of a two-night “America’s Got Talent” finale and the season premiere of “Parenthood” lifted NBC to victory on the final Tuesday before the start of the TV season. CW did OK, by its low-bar Tuesday standards, with its bows of “One Tree Hill” and “Life Unexpected.”

According to preliminary nationals from Nielsen, “America’s Got Talent” dominated the 9 o’clock hour (3.8 rating/11 share in adults 18-49, 14.3 million viewers overall), rising year to year, doubling its lead-in from gameshow “Minute to Win It” (1.9/6 in 18-49, 6.5 million viewers overall) and standing as the night’s clear No. 1 program in key demos as well as total viewers. It was followed by the second-season premiere of “Parenthood” (2.7/8 in 18-49, 7.7 million viewers overall), which was slightly above its rookie-season average and easily led its 10 p.m. hour.

Of course, “Parenthood” — which became the timeslot leader among adults 18-49 down the stretch of its first season — faced much softer competition last night (a low-rated ABC newsmag and a very weak CBS special) than it will face during the coming season, when it will go up against dramas on both ABC and CBS.

ABC ran second to NBC in demos Tuesday behind the season finale of “Wipeout” (slot-leading 2.8/9 in 18-49, 7.6 million viewers overall), which was followed by a special second original episode that placed second at 9 o’clock (2.6/7 in 18-49, 6.1 million viewers overall). The net then fell off with the special news program “Final Witness” (1.4/4 in 18-49, 4.8 million viewers overall).

CW got the jump on its major-network competition by launching the season of vet “One Tree Hill” (1.1/4 in 18-49, 2.2 million viewers overall) and second-year drama “Life Unexpected” (0.8/2 in 18-49, 1.7 million viewers overall).

“Hill,” now in its eighth season, was within about 10% of its year-ago premiere on Monday and delivered the timeslot’s largest overall audience since last October. In key demos, “Life” outperformed the final eight episodes of last season’s low-rated “Melrose Place” in the time period and also delivered the timeslot’s largest overall audience in a year (last season’s second episode of “Melrose”).

At Fox, repeats of last season’s final two episodes of “Glee” averaged a 1.6/5 in 18-49 and 4.5 million viewers overall at 8 p.m. and a 1.8/5 in 18-49 and 4.7 million viewers overall at 9 — higher than the show’s recent encore deliveries.

Similarly, CBS saw week-to-week improvement for its repeats of last season’s finales of “NCIS” (1.8/6 in 18-49, 10.5 million viewers overall) and “NCIS: Los Angeles” (1.5/4 in 18-49, 8.2 million viewers overall). But the net struck out at 10 p.m. with the special “Fashion’s Night Out 2010” (0.6/2 in 18-49, 3.0 million viewers overall).

Preliminary 18-49 averages for the night: NBC, 2.8/8; ABC, 2.3/7; Univision, 1.8/5; Fox, 1.7/5; CBS, 1.3/4; CW, 0.9/3.

In total viewers: NBC, 9.5 million; CBS, 7.2 million; ABC, 6.1 million; Fox, 4.6 million; Univision, 4.2 million; CW, 2.0 million.