HALLANDALE BEACH, Fla. -  Trainer Brendan Walsh posted his first career winner when he sent out Sandcastle to upset Friday’s fifth race at Gulfstream, a maiden special weight dash for older fillies and mares. Walsh had previously served as an assistant to Eddie Kenneally before striking out on his own last year. Sandcastle is a 4-year-old daughter of Mizzen Mast. She was bred in Massachusetts by her owner, Mrs. James Moseley. “It’s a dream of a lifetime to train a winner,” said Walsh. “To have one here is fantastic.” Walsh, 38, currently has a 10-horse stable at Palm Meadows led by Santiva, who was beaten only three lengths in the Grade 3 Ft. Lauderdale on Jan. 14.