Alvarado was originally to be named Rafael Alvarado Jr. but when his father went to register the name it came out Junior Rafael Alvarado and he's been called Junior ever since. He started riding in America in South Florida about 3 1/2 years ago. He thought about returning to Venezuela but decided to come to Chicago at the urging of trainer Moises Yanez, for whom he has ridden with considerable success.
Junior made a big splash in his first meet at Arlington in 2008, winning 81 races to finish eighth in the standings. After the 2008 Arlington meet, he went to Hawthorne for a time before returning to Venezuela. He returned to the United States in time for the 2009 Arlington meet and jumped to the head of the class in his second meet at Arlington, taking the 2009 riding title with 110 wins, three more than James Graham. He won three stakes races at the meet in the Illinois Owners Stakes with Voy Por Uno Mas, the Sea Erin with Public Speaker and the Grade III Arlington-Washington Lassie aboard eventual Eclipse Award winning 2-year-old filly She Be Wild.
In his bid to repeat as riding champion, Junior finished second to Michael Baze in the standings with 97 victories. However, he scored the biggest win of his young career when he guided Richard L. Duchossois Éclair de Lune to victory in the Grade I Beverly D. Stakes.