Happy endings are rare in this mean old world, with grand finales even more elusive. As dusk begins to fall on Halloween, American Pharoah will try to gallop off into the sunset in triumph.

The first Triple Crown winner in 37 years will be favored to win his last race, the $5-million Breeders' Cup Classic, Saturday at Keeneland in Lexington, Kentucky. He'll be facing by far his most challenging field ever in his first try against older horses.

The main threats are the champion mare Beholder, who crushed males in the Pacific Classic at Del Mar; Tonalist, who took the 2014 Belmont Stakes and two Jockey Club Gold Cups, and Honor Code, who earned Met Mile and Whitney trophies. Pharoah's fellow 3-year-olds may be just as dangerous. He'll also have to outrun Keen Ice, the only horse to beat him this year; Belmont runner-up Frosted, whose relentless pressure weakened Pharoah in the Travers, and Gleneagles, a four-time Group I winner on turf in England and Ireland.

"There's a lot of tough horses in here, and that's what the Breeders' Cup is supposed to be," American Pharoah's trainer, Bob Baffert, said. "You have to come to it with your 'A' game, break well and get the trip."

Starting with his season debut March 14 at Oaklawn Park in Arkansas, American Pharoah became a mainstream obsession with seven knockout performances at six racetracks in five states. Even in his second-place finish Aug. 29 in the Travers at Saratoga, he ran gallantly.

"It takes a brilliant, special racehorse to stand up to all he's been through," Baffert said. "He's been able to withstand so much. In the olden days, they used to call horses like him hickory. He's a lean, mean, fighting machine."

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Yet even machines wear down from overuse, and the grind finally got to owner-breeder Ahmed Zayat's iron horse.

"After Saratoga, you could see it was kind of taking a toll on him," Baffert said, "and it took about 30 days for him to bounce back from the Travers."

A series of excellent workouts at Santa Anita have convinced Baffert that Pharoah is as good as ever. His effortless breeze Tuesday morning -- 6 furlongs in 1:10.80 -- fired up the 62-year-old Hall of Famer. "He really looked fantastic," he said, "and I really feel good about the way he's coming into this race.'"

Longtime Southern California clocker Gary Young was dazzled, too. "This work was terrific," Young said. "I think he's a great horse who's going to be very tough to beat."

The workout also aroused bittersweet feelings in Baffert. "This was the last serious drill of his life," he said. "It's sort of sad in a way to think that's the last time we get to see him work like that."

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American Pharoah is scheduled for an easy half-mile breeze on Monday, the day before shipping to Kentucky.

Win or lose, the Pharoah tour will end with a van ride to nearby Versailles, where the colt will begin his stallion career during the winter at Ashford Stud. To Baffert, "his legacy has been made," but he still wants his horse of a lifetime to go out on top.

Baffert has won dozens of world-class races, including the Kentucky Derby four times and last year's Classic with Bayern. Yet all that success won't banish the butterflies late Saturday afternoon.

"I think all the trainers are on pins and needles," he said. "Horses are like children, they can get cut or do something . You're never safe until you put that saddle on. That's why I have three stents in my heart.''