A huge turnout for the two-hour season finale of “CSI” powered CBS to a dominant victory on the final Thursday of the season, according to preliminary nationals from Nielsen. Along with a solid showing at 10 by “Without a Trace,” the Eye logged its best Thursday in demos since February 2003.

From 8 to 10, “CSI” (10.4 rating/28 share in adults 18-49, 30 million viewers overall) uncorked its biggest May sweep perf ever, picking up steam with each half-hour and doubling up NBC’s “The Apprentice 3” finale (6.1/15 in 18-49, 13.7 million viewers overall) in its concluding hour.

At NBC, “Will & Grace” ended its season with modest numbers for a one-hour episode (3.5/10 in 18-49, 7.9 million viewers overall). “The Apprentice” picked up from there but was well behind the finales for its previous two editions, and “ER” (8.6/22 in 18-49, 18.6 million viewers overall) moved ahead at 10 in key demos opposite the Eye’s “Without a Trace” (7.0/18 in 18-49, 21.9 million viewers overall).

Fox enjoyed one of its best Thursdays of the season with the season finale of “The OC” (3.4/10 in 18-49, 7.5 million viewers overall) and a special “American Idol” (3.9/10 in 18-49, 8.1 million viewers overall) focusing on the worst auditions of international editions of the megahit.

ABC was about on par with the NBA playoff game between the Detroit Pistons and Indiana Pacers (2.1/5 in 18-49, 5.4 million viewers overall).

Preliminary 18-49 averages for the night: CBS, 9.2/24; NBC, 6.1/16; Fox, 3.7/10; ABC, 2.1/5; UPN, 1.5/4; WB, 1.1/3.

In total viewers: CBS, 27.3 million; NBC, 13.4 million; Fox, 8.1 million; ABC, 5.4 million; UPN, 4.2 million; WB, 2.8 million.