NEW YORK — Many viewers were first acquainted with Ashley Jensen when she played Maggie, the dowdy, dim-bulb sidekick to Ricky Gervais on his show-biz spoof “Extras.”

Then, she landed a plum supporting role on ABC’s “Ugly Betty” as Christina, the worldly-wise wardrobe mistress for a high-fashion magazine.

Those characters, past and present, are quite different. Not so different: What it took for Jensen to portray them, she says.

“It’s amazing what a bit of makeup and standing up straight can do,” she volunteers in her plush Scottish accent.

To demonstrate, she droops into Maggie’s identity (slouching in her chair, with a vacant gaze), after which, as Christina, she snaps to high alert (recommended for surviving the predatory culture that pervades the offices of Mode magazine on “Ugly Betty”).

To play Christina, “You just sit up,” explains Jensen, “and close your mouth when you’re thinking.”

With the series’ third season (premiering at 8 tonight), production of “Ugly Betty” has moved cross-country to New York, where the story had always been set.

Now, its eye-popping studio shots can be supplemented with location scenes all over real-life Gotham, making the show more visually stylish than ever.

Not only has “Ugly Betty” uprooted itself from Hollywood. So did its large company of actors — except Jensen.

“I shuttle over here for a couple of days, then shuttle home again. But don’t take that as an insult,” she adds, as if to assuage any sensitive New Yorkers. “It was only because I had done the great big move with my husband (actor Terence Beesley) and my dog from London to L.A. two years before.”

They found a rental ideally located in the Hollywood Hills near two parks, the better to accommodate their 100-pound pooch Barney.

They have since bought a house and fetched their furniture from storage in England. Barney is happy. The family feels settled.

“But I still feel like I’m on holiday,” Jensen confesses. “When I first arrived, I had a suitcase full of sarongs and bikinis. I didn’t have one jumper. I still look at the Hollywood sign and think: What am I doing here?”

What she’s doing, of course, is a hit series, where she’s pleased to be appearing alongside its star, America Ferrera, whom she describes as “a delightful young woman, a good soul who’s on the right track — and she’s not gonna go giddy with it.”

In short, Jensen, 39, has come quite a distance from the Scottish town of Annan, where she grew up.

“I had a great life there,” she recalls. “My ambition was never really to get the hell out of that place, and it was never, never to be in Hollywood! I just knew that I wanted to act and tell stories.”