– Kentucky Derby favorite Justify will not only have to outrun the 20-horse field at Churchill Downs on Saturday, he also will have to contend with “The Curse of Apollo.”

What is “The Curse of Apollo?”

No horse who went unraced as a 2-year-old has won the Kentucky Derby since one named Apollo — in 1882. That’s 136 years.

This year, two horses have the distinction — the 3-1 morning-line favorite Justify, trained by Bob Baffert, and 6-1 third choice Magnum Moon, trained by Todd Pletcher.

“There’s probably a number of reasons for it, and inexperience could be part of it,” Pletcher said of the unraced 2-year-olds’ futility. “It always helps in these situations to have a little bit of seasoning, experience and [proven ability to] overcome some adversity. But I think when the right horse comes along it will happen.”

Since 1937, 61 horses unraced at age 2 have entered the Kentucky Derby. Only two, Bodeimeister in 2012 and Air Forbes One in 1982, entered the gate as favorites. Bodemeister finished second to I’ll Have Another. Air Forbes One finished seventh.

Perhaps the most famous and successful horse to fall to the curse was Curlin in 2007. While he finished third behind Street Sense and Hard Spun at the Derby, he went on to win back-to-back Eclipse Awards as Horse of the Year in 2007 and 2008 with wins in the Preakness and Breeders’ Cup Classic on his resume. And he’s gone on to a stellar stud career with three sons entered in the Derby this year: Good Magic, Solomini and Vino Rosso.

James Scully, a racing analyst with TwinSpires.com, believes the curse most certainly will fall soon and this year represents the best chance, yet.

“These are the most talented Apollo horses and we have two of them,” Scully said. “We’ve had Bodemeister, and we’ve had Curlin who ran second and third and ran well, but we’ve never had two horses like Magnum Moon and Justify not run a race at 2.”

Since the advent of the Kentucky Derby points system in 2013, races for 2-year-olds don’t count for much toward Derby hopes. The new emphasis is on how you race in March and April before the Derby.

That’s also meant horses are racing less coming into the Derby. Eight of the 20 horses Saturday have raced fewer than five times. Justify is one of two horses that have raced only three times.

“Back in the old days, horses running seven times didn’t seem to be enough,” said jockey Mike Smith, who will guide Justify on Saturday. “They are a lot more lightly raced [now]. You’ll see horses who haven’t run at two win the Derby more often.

“Hopefully, this year.”