Oddsmaker Russ Hudak made the 5-year-old mare the 5-2 morning line favorite after she drew post position No. 9 in the field of 10 on Wednesday.
Catch a Flight, who like Beholder is trained by Hall of Famer Richard Mandella, was the second choice in the 1 1/4-mile race on dirt for 3-year-olds and up.
The field also included Hard Aces, the winner of the Grade I Gold Cup at Santa Anita Park on June 27, and Bayern, winless in three starts since winning the 2014 Breeders' Cup Classic.
Hard Aces was the co-third choice at 5-1 with Hoppertunity, while Bayern was the co-fifth choice at 6-1 with Red Vine.
Mandella decided to enter Beholder in the Pacific Classic following her seven-length victory in Del Mar's Grade I $300,000 Clement L. Hirsch Stakes on Aug. 1.
“I think when you come to a point when you're winning in your own class so much, you probably ought to try something different,'' Mandella said. “It has been pretty easy for her for a year and she's not over-raced, so I think there's nothing wrong in trying and I'm pretty confident in her. She's pretty good.''
The Pacific Classic was the first time Beholder has run against males. The 1 1/4-mile Pacific Classic was one-eighth of a mile farther than Beholder has run before.
“She's a sweetheart in the stall, but when she steps on the track, she becomes a man,'' said Hall of Fame jockey Gary Stevens, who rode Beholder for her 10th consecutive race. “I go along for the ride. She puts me where I want to be and when I push the button, she responds.''
Beholder became the fifth female to race in the 25-year history of the Pacific Classic. Paseana was the first, finishing fifth in 1992, still the best result for a female runner.
Beholder carried 119 pounds, five pounds less than each of the other entrants.