NEW YORK — She is a hot dog, this little Sadie.

Tongue out and wagging tail up, the perky, 4-year-old Scottish terrier has won more than 100 best in show ribbons and is the overwhelping favorite to complete dogdom's Triple Crown this week at Westminster. She's already charmed the judge, in fact.

What in the show world could go wrong for America's top dog at America's top pooch pageant?

Well, plenty.

Two years ago, she got spooked at Madison Square Garden. Her handler's new shoes were too squeaky, the wooden boards covering the ice hockey rink thumped too loudly. There was a stray TV monitor that threw her, too.

Then last February, she had a potty accident on the green carpet while coming out to take her place in the final ring.

Come Tuesday night, it could be Sadie's turn. Or not. Because inside those purple and gold ropes, the show world revolves around one guiding principle.

Dog on the day.

"That's what we always say," said David Frei, longtime host of the Westminster telecast on the USA Network and CNBC. "It doesn't matter what you've done in the past. It's what you do inside that ring on any given day."

So maybe there's room for another contender, perhaps a prize Doberman pinscher, a familiar puli or a sweet golden retriever.

Dogs from 173 breeds and varieties begin competing Monday morning, with three newcomers to Westminster: the Irish red and white setter, the Norwegian buhund and the Pyrenean shepherd.

There are a full 2,500 entries — up from last year, when a slow economy took a bite out of the show — including a 12-year-old shiba inu and 10-month-old miniature bull terrier. Australian shepherds are the most popular with 44 while there were just two kuvaszok.

The hound, toy and nonsporting groups will be judged Monday. The sporting, working and terrier groups go Tuesday. Then shortly before 11 p.m., judge Elliott Weiss will make his pick for best in show.

Chances are, Weiss will see Sadie among the final seven — oddsmaker John Avello playfully lists her as the easy 8-to-1 favorite at the Wynn Las Vegas casino.

Weiss chose Sadie as best in show at an event in North Carolina in September. It's common for top judges to see the best dogs at competitions around the country during the year.

Plenty of judges have picked the coal-black Sadie, whose registered name is Roundtown Mercedes of Maryscot. She won the prestigious National Dog Show in November and the AKC/Eukanuba National Championship in December.

"Incredible," praised Clint Livingston, handler of a golden retriever called Treasure who is the country's No. 4-ranked show dog.

Sadie got rankled during terrier judging at Westminster in 2008 and was the runner-up. Trying to prepare her for all sorts of future distractions in the big ring, handler Gabriel Rangel took to having strangers feed her treats.

Last year at the Garden, Sadie won the terrier group. "Maybe I should take a Scotch," Rangel said.

An underdog, so to speak, wound up winning best in show. Crowd favorite Stump, a 10-year-old Sussex spaniel, took the ribbon and silver bowl. He's now retired, living a dog's life in Texas.

Scotties have won best in show at Westminster seven times, surpassed only by 13 wins for wire fox terriers. Then again, not since a perfectly primped bichon frise called J.R. in 2001 has America's reigning No. 1 show dog won Westminster.

"Dog on the day," Frei said.