An extreme longshot, Repent, came from the back of the 12-horse field to finish second and Siphonic, caught on the rail in the stretch, was third. Officer, after leading into the turn, finished fifth.
Johannesburg is trained by Aiden O'Brien. The Kentucky-bred son of Hennessey had won all six starts in Europe this year but had never raced beyond six furlongs. He finished Saturday's 1 1/16 mile in 1:42.27.
O'Brien and his camp brought a huge entourage, all of whom greeted Johannesburg as he returned from the race, many waving Irish flags.
Johannesburg paid $16.40, $8.60 and $6; Repent $25 and $13.40; Siphonic $7.90. The $2 exacta paid $530.
Officer, who had won all five of his previous starts, battled for the lead with Came Home until the field entered the turn. He then gave way easily.
"It was not his day today. In his next race, he'll come back and prove to everybody that he's a champion," Espinoza said.
Baffert can take consolation from the fact that no Breeders' Cup Juvenile winner has ever come back the following year to win the Kentucky Derby.