Royal Delta and jockey Mike Smith finished fourth as the 7-5 favorite in the Distaff.
At 50, Stevens began a comeback in January that has included winning the Preakness Stakes. He earned his ninth career Cup win and first since 2000.
Beholder, last year's champion 2-year-old filly, put herself in position to claim this year's 3-year-old filly title.
"She's the most intelligent animal that I've ever been around," Stevens said. "She listens. She doesn't always obey, but when she's in a race, she listens to what I want to do and the lessons that she's been taught."
Beholder's owner, Public Storage founder B. Wayne Hughes, credited Stevens.
"Having a comeback like he's done at his age is phenomenal," he said. "We really have one of the greatest athletes on the planet sitting right here who is saying the horse is smarter than him, OK?"
It was a good day for the older guys.
Smith, a 48-year-old Hall of Famer, won two of the five Cup races at Santa Anita, and will be aboard early favorite Game On Dude in the $5 million Classic on Saturday.
"We're just two old athletes that are still applying our trade pretty good," Stevens said.
Still, he couldn't resist zinging his longtime friend.
"I'm so proud of Mike," Stevens said, "even if he did shut me off in one of those races."
Beholder ran 11⁄8 miles in 1:47.77 on her home track, where she is trained by Richard Mandella. This weekend marks the 10th anniversary of Mandella winning a record four Cup races in a single day at the 2003 world championships.
Beholder paid $7.60, $4.20 and $3.20.
Close Hatches returned $6.60 and $4.80, while Authenticity was another 1¾ lengths back in third and paid $4.20 to show.
Street Girl was fifth and Princess of Sylmar last in the field of six.
Royal Delta was trying to join Goldikova as the only three-time winners of a Cup race.
"She didn't have it today. No spark, man," Smith said. "She usually takes the race to somebody, but not today. I thought when Beholder come up to her, she would pick it up, but she didn't."
"I'm kind of dumbfounded," he said.
Four jockeys and five trainers won each of the Breeders' Cup races in front of 35,833 fans on a sunny, cloudless day with the temperature in the 80s. Attendance was up 1,214 over last year's Friday total.
Smith triggered the day's biggest upset in the $500,000 Marathon, the first of five Cup races. He guided London Bridge to a length victory that was worth $20 to win.
Smith followed it up with a length victory aboard Britain-bred Outstrip in the $1 million Juvenile Turf, extending his record for most Cup wins by a jockey to 19. Smith is already the event's leader among money won with more than $23 million.
Goldencents snapped a five-race skid by winning the $1 million Dirt Mile for co-owner Rick Pitino, the Louisville basketball coach who wasn't on hand to join the raucous winner's circle celebration.
Rafael Bejarano rode Goldencents to a three-length victory. It was the fourth Cup win and first since 2007 for both him and trainer Doug O'Neill. Goldencents' skid included a 17th-place finish in the Kentucky Derby and a fifth-place in the Preakness when Kevin Krigger was his rider.
Ireland-bred Chriselliam won the $1 million Juvenile Fillies Turf, giving jockey Richard Hughes and trainer Charles Hills their first Cup victories.
The 2-year-old filly paid $15.80 to win. Her owners include retired star jockey Willie Carson and Chris Wright, the founder of music publishing giant Chrysalis.
Breeders' Cup Distaff
5 Beholder (G.Stevens) 7.60 4.20 3.20
3 Close Hatches (J.Rosario) 6.60 4.80
2 Authenticity (J.Velazquez) 4.20
Off 4:42. Time 1:47.77. Fast. Also Ran • Royal Delta, Street Girl, Princess of Sylmar. Pick 6 (5-7-4-12-8-5) 6 Correct Paid $106,839.80, 5 Correct Paid $1,128.80. $0.5 Pick 4 (4-12-8-5) 4 Correct Paid $403.90. $1 Pick 3 (12-8-5) 3 Correct Paid $160.00. $1 Superfecta (5-3-2-4) paid $219.90. Daily Double (8-5) paid $53.00. $1 Exacta (5-3) paid $21.30. $1 Trifecta (5-3-2) paid $87.80.