Casino Drive could be an obstacle for Big Brown’s Triple Crown hopes

A chance to make history in the Belmont Stakes in New York awaits Big Brown if he manages to win the Preakness on Saturday at Pimlico.

Casino Drive will also be waiting for the son of Boundary on the first Saturday in June in the final leg of the Triple Crown at Belmont Park.

Should Big Brown vanquish his opponents in Baltimore later this week, his biggest obstacle to becoming the sport’s first Triple Crown winner since Affirmed in 1978 figures to be Casino Drive.

A son of Mineshaft, the 2003 horse of the year, Casino Drive had an auspicious U.S. debut Saturday, easily winning the $200,000 Peter Pan Stakes at Belmont. A $950,000 yearling purchase in 2006 by owner Hidetoshi Yamamoto, Casino Drive had started his career in Japan with an 11 1/2 -length victory versus maidens as the 1-5 favorite Feb. 23 at Kyoto.

Although the margin of victory was considerably smaller, Casino Drive was equally impressive in the Peter Pan. He won by 5 3/4 lengths under Kent Desormeaux, who is also the rider of Big Brown. Agents of other big-name jockeys were probably calling during the stretch run of the Peter Pan hoping to get their client on the latest wonder horse, on June 7.

Should Big Brown lose Saturday, he would almost certainly skip the Belmont, freeing Desormeaux to stay with Casino Drive, who will have a family tradition to live up to in 25 days.

The colt is out of the mare Better Than Honour, which makes him a half-brother to Jazil and three-quarter brother to Rags To Riches, the last two winners of the Belmont.

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The Jim Murray Memorial Handicap, which was won for a second year in a row by 9-1 shot On The Acorn, wasn’t the only stakes race run Saturday at Hollywood Park.

The card also featured a narrow – and controversial – victory by Sweeter Still in the Senorita and an extremely impressive victory by Street Boss in the Los Angeles Handicap.

In winning for the third time in her last four starts, Sweeter Still had to survive a stewards’ inquiry after edging Magical Fantasy in the Grade III. The call was a difficult one and the stewards made no change, saying both horses drifted out nearing the wire.

Yet on Sunday, the same stewards decided to hand Martin Garcia, who rode Sweeter Still, a three-day suspension. A suspension, but no disqualification? This type of double standard is why so many fans and observers are constantly frustrated by the decisions made by the stewards on the local circuit… .

Despite clipping heels shortly after the start, Street Boss was able to re-gather himself under new rider David Flores and rally to win the Los Angeles, giving him four wins in his last five starts for trainer and part owner Bruce Headley.

It was the first graded victory for the 4-year-old Street Cry colt and, at this point, he looks to be one of the country’s top sprinters and a legitimate threat in the Breeders’ Cup Sprint, which will be run Oct. 25 at his home track, Santa Anita… .

Another 3-year-old to keep an eye on in the coming months is Unbridled’s Heart. A $1-million yearling purchase at the same Keeneland sale that produced Casino Drive, the son of Unbridled’s Song defeated maidens by 10 lengths Saturday at Belmont. Javier Castellano rode the gray for owner Darley Stable and trainer Tom Albertrani and it will be the last time anybody gets nearly 14-1 on the colt… .

Harlem Rocker, who is undefeated in three starts, will not challenge Big Brown in the Preakness. Owned by breeder Frank Stronach and trained by Todd Pletcher, the gray son of Macho Uno will instead point to the $1-million Queen’s Plate on June 22 at Woodbine in Toronto.

A winner twice at Gulfstream Park and successful in his New York debut in the Withers on April 26 at Aqueduct, Harlem Rocker was bred in Canada, so it makes sense to try him in the Plate, which is the first race of the Canadian Triple Crown.

bob.mieszerski@latimes.com