Giant Oak, fully recovered from a mouth injury that cost him a work on Feb. 28, tuned up for his start in the Louisiana Derby with a strong five-furlong drill on Saturday morning at Fair Grounds. Giant Oak, a wide second to Beethoven in the Kentucky Jockey Club Stakes in his final start at 2, and a troubled fifth in the Risen Star Stakes at Fair Grounds in his 3-year-old debut, was timed in 1:00.80 for five furlongs, the second-fastest among 36 works at the distance Saturday.\nAboard the strapping chestnut colt, as he has been for every Giant Oak work this winter in New Orleans, was jockey James Graham.\n"It was perfect," Graham said of the breeze. "You couldn't have asked for anything more."\nGraham said that he has seen improvement in Giant Oak over the course of the last couple months.\n"He's got a little more mature," said Graham. "He's just a big child, really. He's not playing around as much as he used to."\nGraham has never ridden Giant Oak in a race, but will get the chance Saturday when he replaces Edgar Prado, who was aboard for the Risen Star. Graham is having his usual solid meet at Fair Grounds, but he more often has been in the position of losing talented mounts to bigger-name riders than picking them up for major races.\n"I'm just glad to get the opportunity," Graham said. "Now I have to make the most of it."\nGiant Oak was not the only highly regarded 3-year-old working Saturday. Silver City drilled one mile in a strong 1:39. Silver City is headed to Oaklawn Park this week to start in the Rebel Stakes there on Saturday.\nDiamond Tycoon out of Muniz\nSaturday's $500,000 Mervin Muniz Handicap lost a major player when the explosive turf runner Diamond Tycoon suffered a soft-tissue injury. Diamond Tycoon worked five furlongs on Wednesday, and at first appeared to have come out of the work in good order, but later in the day a problem was detected, and now Diamond Tycoon is out of action indefinitely, trainer Andrew McKeever confirmed Saturday.\nDiamond Tycoon, who raced in England early in his career, already had won three turf races at the Fair Grounds meet, most recently capturing the Grade 3 Fair Grounds Handicap with a powerful late run.\n"I thought he was a Grade 1 kind of horse," McKeever said.