As pop-culture watchdogs, it is our custom to make certain that no celebrities get too big for their britches. If any of them get too powerful, it's our sworn duty to drag them back down to Earth.

With that tradition in mind, it's about time for Tina Fey's stumble. In the past six months, she has written the underrated summer gem "Baby Mama," been elected president of Sarah Palin impersonators and taken home three Emmys as a writer, producer and actress. If anyone needs a dose of humility, she does.

So it's with a tinge of disappointment that I must report that Fey remains fabulous.

Her sitcom, "30 Rock," kicks off its third season Thursday and quickly assures us that the show named best comedy two years in a row hasn't missed a beat.

The opening scene is cause for alarm as Fey struts down the street in a gorgeous flower dress with background music that sounds lifted from the "Sex and the City" soundtrack.

When she didn't get splashed by a bus, I thought that Fey's recent success had convinced her that she was a glam girl. I should have known better.

"Did the people from that makeover show finally respond to your letter?" says her puzzled former boss, Jack (the masterful Alec Baldwin, who immediately makes up for his amateurish turn last week on "Saturday Night Live").

We soon learn that Fey's character, Liz Lemon, the head writer of a comedy sketch series, is only dolled up to impress a representative from an adoption agency, a role played by Megan Mullally.

Mullally, the former "Will & Grace" star, is part of a parade of well-known celebrities, including Salma Hayek and Jennifer Aniston, who will stop by this season. High-voltage guest stars often serve as distractions, stealing the light from the core cast, but Mullally more than willingly sinks to the show's goofball level, allowing stylists to give her a hair bun so tight that it could break concrete, while Fey slowly dissolves into the mess we love.

Next week's guest could have been even more problematic. That's because it's Oprah Winfrey, a catch that might have caused some series to pull their punches and tread lightly. Instead, "30 Rock" comes up with one of its most politically incorrect episodes, which dares to include one white character dressed in blackface. (Trust me: It's hilarious.) Winfrey herself is beyond a good sport, revealing that her new "favorite things" include Chinese checkers and calypso, and urging Lemon to keep her hands outside of her clothes during a long hug.

To give away more would be criminal, except this: Fey's roll continues. We'll have to wait until "Mean Girls 2: The College Years" before we start raining on her parade.

njustin@startribune.com • 612-673-7431