The cavalry will be coming after Rock Opera Saturday as the field turns into the homestretch of the Del Mar Derby. The son of Royal Academy, who went gate to wire to win a division of the Oceanside Stakes on Del Mar's opening day, is pretty much a sure thing to be on the lead again if he breaks sharply in the 1 1/8-mile trip on the Jimmy Durante Turf Course.Trainer Clifford Sise, who acknowledges he's never had a grass runner of this magnitude, is hoping that his 3-year-old gelding's speed will hold over a course that has been playing to come-from-behind runners.All of the Derby entrants who have posted wins, save Rock Opera, prefer to come from the off the pace. If Rock Opera is up to the challenge – and he has three wins in four career starts to show for his determination – he could be hard to run down.Set to take on Rock Opera are the probable favorite, Inesperado, winner of Del Mar's La Jolla Handicap (gr. IIT); and Mr. Mellon, winner of the Arlington Classic (gr. IIT). Others are:* True Phenomenon, winner of the other Oceanside division;
* Dell Place, who won Del Mar's Relaunch Stakes;
* Golden Arrow, winner of two straight but making his debut at the stakes level;
* Johar, who has lost his past three races by a total of 1 1/2 lengths;
* Mountain Rage, who won three straight on the Santa Anita turf during the winter;
* and Hecandigit, a non-winner who put a final work of 3 furlongs in 35 flat this morning for trainer Warren Stute. The latter already has won four stakes, three of them graded, at the seaside this season.