Her defection leaves Music Note as the early 9-5 favorite in the eight-horse field for the 1 1/8-mile Ladies’ Classic today at Santa Anita. The $2 million race is the highlight of six Breeders’ Cup races on Day 1, five of them featuring females, with the $500,000 Marathon for males.

Zenyatta’s presence in tomorrow’s $5 million Classic is daunting to some of her rivals.

“I would have entered her with the fillies so I didn’t have to run at her,’’ said Chip Woolley Jr., who trains Kentucky Derby winner Mine That Bird.

“She’s going to be running late and she has a lot of style, much the same as my horse. She’s twice his size, so if she decides to knock him out of the way, she’s got a good chance.’’

Zenyatta is going against male competition for the first time in her career. She will break from the No. 4 post in the 1 1/4-mile race. “Optimism is high,’’ said Jerry Moss, who owns the 5-year-old mare with his wife. “I think everybody is in for a treat.’’

Zenyatta is grabbing the attention in the absence of Rachel Alexandra, who was 8 for 8 this year, including three wins over male horses. Owner Jess Jackson shut her down for the season because he dislikes Santa Anita’s synthetic track.

No female horse has won the Classic in its 25-year history. Zenyatta will be the fourth female to try. Jolypha had the best result, finishing third in 1992.

Zenyatta would have been the closest thing to a sure bet in the Ladies’ Classic. Without her, Music Note will try to improve on last year’s third-place finish. Careless Jewel is the early second choice at 2-1. She comes in on a five-race winning streak, with only one loss in her career for Josie Carroll, who would be the first female trainer to win the race. The 3-year-old gray filly will break from the No. 1 post and likely use her tactical speed to go to the lead.

Even without Zenyatta, trainer John Shirreffs still has a horse in the Ladies’ Classic with Life is Sweet, who has fruitlessly chased Zenyatta in three of her last four races.

“It breaks my heart that Zenyatta is not in the race,’’ owner Marty Wygod said, jokingly.

The $500,000 Marathon begins today’s races, with gelding Cloudy’s Knight making his Breeders’ Cup debut at age 9.

European horses won five of last year’s 14 races, and could make a strong showing again. Ireland-bred Lillie Langtry, trained by Aidan O’Brien, is the 3-1 early favorite in the $1 million Juvenile Fillies Turf.