BALTIMORE—Tragedy came fast on Preakness Stakes day, with two horses dying within the first four races at Pimlico Race Course.

Homeboykris, a 9-year-old gelding, collapsed after winning the day’s first race, run at 1 1/16 miles on dirt. Then in the fourth race, Pramedya, a 4-year-old filly, was euthanized after suffering a fractured left front cannon bone in the fourth race, run at 1 1/16 miles on turf.

Officials...