The Bob Baffert-trained six-year-old was partnered by the Italian to glory in the Dubai World Cup in March last year, and Dettori was reunited with the son of Tonalist when he kicked off his spell riding in Santa Anita on Boxing Day.
Country Grammer could hardly have looked better in landing short odds in the Grade Two San Antonio Stakes, on a night where Dettori struck three times from five rides.
Baffert - whose Charlatan was upset by Mishriff in the inaugural running of the world's most valuable race - can also call on the high-class Taiba, a Grade One winner on the same Santa Anita card courtesy of the Malibu Stakes.
Further strength to the American challenge could come in the shape of Kentucky Derby hero Rich Strike, while last year saw a shock success for the locally-owned and trained Emblem Road who may well return to defend his crown.
A second victory would make the son of Quality Road the highest-earning thoroughbred in history with $20.2million to his name, ahead of Australian wondermare Winx who totalled $18.3m by the end of her record-breaking career.
George Boughey's Missed The Cut is engaged for Britain, as is John and Thady Gosden's Mostahdaf, the Charlie Appleby-trained Rebel's Romance, Jane Chapple-Hyam's Saffron Beach, William Knight's Sir Busker and Simon and Ed Crisford's hugely impressive Dubai winner Algiers.