In the Derby, he had to surmount what came to be known as "Curse of Apollo" – a reference to the fact that no horse had ever won the Derby without racing while at age two since Apollo in 1882. "Justify is a natural and he's still green, just learning how to run. He's so talented," said his trainer Bob Baffert. "But there are a lot of nice horses out there this year." Trainer Todd Pletcher, who won the 2017 Kentucky Derby with Always Dreaming, had four of the leading contenders: Magnum Moon, Audible, Vino Rosso, and Noble Indy. Magnum Moon was ranked number two on the National Thoroughbred Racing Association top three-year-old poll of April 16 after his win in the Arkansas Derby. He had made only four starts prior to the Kentucky Derby, like Justified not having raced at age two. Audible was ranked number three, while Vino Rosso and Noble Indy were ranked seventh and eighth respectively. The two colts with the best form at age two, Good Magic and Bolt d'Oro, were ranked fourth and fifth respectively on the same poll. They were the winter-book favorites for the Derby, but both suffered training setbacks that delayed their return to the racetrack. They both had one win from two starts at age three going into the Derby. Adding an international element to the field was Mendelssohn, trained in Ireland by Aidan O'Brien. Mendelssohn started his racing career on the turf and proved his ability to ship well by winning the Breeders' Cup Juvenile Turf at Del Mar in California in 2017. However, O'Brien felt that the colt would be equally suited to racing on the dirt given his pedigree: Mendelssohn is a half brother to multiple Eclipse Award-winner Beholder. Mendelssohn earned his berth by winning the UAE Derby in an "astonishing" performance while setting a track record. Entries for the Kentucky Derby were taken on May 1. Justify drew post position 7 and was installed as the 3-1 morning line favorite by oddsmaker Mike Battaglia. Because the Derby was held on a rainy day, the surface of the track was sealed to mitigate the effect of heavy rain on the footing. Nonetheless, the track condition was sloppy. By post time, more than of rain had been recorded that day at nearby Louisville International Airport, breaking the Derby Day precipitation record of that had been set in 1918.