Long dominated by NBC, the battle for Thursday nights has been joined. And may already be over. Last week, fewer viewers watched “The Apprentice,” last year’s most talked-about new series, than a repeat of “CSI.”

Tonight, “CSI” (8 p.m., CBS) enters its fifth season and will probably remain the most-watched program in primetime. In the season opener, four separate fatal incidents stretch the team’s graveyard shift to the breaking point. Reiko Aylesworth (“24”) and French Stewart (“3rd Rock from the Sun”) guest star.

ABC and Fox, long uncompetitive on Thursday nights, hope to change that status by scheduling two of their strongest-performing series.

A guilty-pleasure combination of “Queen for a Day” and “Nip/Tuck,” “Extreme Makeover” (7 p.m., ABC) enters its third season with a two-hour installment covering three dramatic transformations involving sisters afflicted with cleft palates and a man hoping to reverse a vasectomy. Now that’s heartwarming.

Fox continues to try to introduce its soapy drama “The O.C.” to as many viewers as possible. Tonight’s special “Welcome to the O.C.: A Day in the Life” (7 p.m., Fox) offers “blooper” clips and interviews with cast members. What’s next? “The O.C.: For Dummies”?

• “ER” (8:59 p.m., NBC) has alienated many longtime fans with plots that emphasize catastrophic situations over character development. Help, it seems, is not on the way. In tonight’s 11th-season premiere, Pratt escapes a gunfight only to find himself submerged in an even stickier situation.
• “Without a Trace” (9 p.m., CBS), enters its third season, a year that may finally see the missing-persons drama overtake “ER” in the ratings. In tonight’s season premiere, Malone’s team hunts for a blind student and her mentor, both kidnapped during a camping trip. Timothy Busfield (“thirtysomething,” “The West Wing”) has joined the series as a co-executive producer and will also appear as Jack’s lawyer.
• Last week, Jennifer Lopez appeared on “Will & Grace” (7:30 p.m., NBC) in a farfetched and laugh-free guest appearance. Tonight, it’s Janet Jackson’s turn. At least she has sitcom experience. This marks Jackson’s first television appearance in an episodic comedy in more than 20 years. Look for a sitcom malfunction.

Tonight’s other highlights

• Lack of fire dampens spirits on “Survivor” (7 p.m., CBS).
• The Donald’s acolytes compete to concoct the right recipe for toothpaste on “The Apprentice” (8 p.m., NBC).