NEW YORK - Saturday is a blockbuster day at Fair Grounds, and it also is the most important day yet when it comes to Kentucky Derby prep races.\nThe Grade 2, $600,000 Louisiana Derby, one of four key Kentucky Derby preps to be decided Saturday, is the main event on a stakes-packed card at Fair Grounds that, among other races, includes three additional Grade 2 events, the $500,000 New Orleans Handicap, the $500,000 Mervin H, Muniz Jr. Memorial Handicap, and the $400,000 Fair Grounds Oaks.\nThe Louisiana Derby also is the richest of the four Kentucky Derby preps on the national schedule, the others being the $300,000 Rebel Stakes at Oaklawn Park (which will mark the second start this year by Kentucky Derby future book favorite Old Fashioned), the $300,000 Tampa Bay Derby, and the $200,000 San Felipe Stakes at Santa Anita. Like the Louisiana Derby, the Rebel, and San Felipe are all Grade 2 races. The Tampa Bay Derby is a Grade 3 race.\nWhile the card at Fair Grounds borders on sensory overload, it is not the only track with multiple stakes on its program. The co-feature at Santa Anita is the Grade 1, $300,000 Santa Margarita Invitational Handicap. There is a stakes doubleheader at Gulfstream Park consisting of the Grade 2, $300,000 Gulfstream Park Handicap and Grade 3, $150,000 Palm Beach Stakes. And like at Fair Grounds, Saturday is the biggest day of the year at Tampa Bay Downs, where the Grade 3, $200,000 Florida Oaks and Grade 3, $175,000 Hillsborough Stakes support the Tampa Bay Derby.\nLouisiana Derby\nFriesan Fire is going for a sweep of Fair Grounds's important 3-year-old stakes, and it would certainly be no surprise if he succeeded. But Papa Clem, Giant Oak, and Flying Pegasus will have their share of supporters. Papa Clem was a sharp second last time out in Santa Anita's Robert Lewis, ahead of I Want Revenge, who was lights out in last week's Gotham. Giant Oak had an awful trip when fifth as the favorite in the Risen Star, and Flying Pegasus was an impressive second in the Risen Star off a layoff and a wide trip from a tough outside post.\nBut as well as Flying Pegasus ran in the Risen Star, it was a demanding effort off a layoff, which suggests he might regress this time. Giant Oak's bad trip in the Risen Star made it impossible for him to show what he can do. Everyone saw it, but few are asking if Giant Oak, even with a good trip Saturday, has ever run a race good enough to win this. It's debatable if he has. And as for Papa Clem, it seems like everyone expects him to freak here in his first career start on dirt like I Want Revenge did in the Gotham. He might, but it's no sure thing. Unlike the dirt-bred I Want Revenge, Papa Clem is somewhat turf bred, which means he also is bred to race up to his abilities on synthetic surfaces. So Papa Clem might not improve nearly as much off the switch to dirt.\nPatena, who will be making his first start for trainer Rick Dutrow, is my pick. Everyone knows how dangerous first-time Dutrow horses are, with This Ones for Phil and his 116 Beyer Speed Figure in the Sunshine Millions Dash being a notable recent example. But Formulator Web trainer stats show just how powerful this angle has been. Over the last two years, horses making their first start for Dutrow have won at a 35 percent clip for a juicy $2.99 return on investment. The numbers get even better when you restrict the sample to dirt races like this one: a strike rate of 40 percent and an ROI of $3.19. And the ROI jumps to $3.52 in graded stakes.\nThe important thing here, however, is Patena doesn't even have to improve that much to beat Friesan Fire. He was a gaining second, beaten only 1 1/2 lengths by that opponent, last time out in the Lecomte. That was Patena's first start on dirt, and, not coincidentally, the best race he's ever run.\nNew Orleans Handicap\nEven though Slew's Tiznow broke from post 13 last time out in the Strub Stakes at Santa Anita, I liked him, and he rewarded me with a next-to-last-place finish. Undaunted, I'm taking him back to post an upset in this spot.\nI think that Slew's Tiznow, after three off-the-board finishes at Santa Anita, just does not like the Pro-Ride surface there. I think trainer Doug O'Neill probably thinks the same thing, which is why Slew's Tiznow is now on dirt in this spot. After all, Slew's Tiznow became a very promising prospect when he notched a big maiden win on dirt at Saratoga at 2. His strong score three starts back in the War Chant at Hollywood Park earned him a Beyer that is competitive with what anyone else in this race is capable of. That race portends a successful transition to dirt. Many players, this one included, believe that of the three synthetic racing surfaces in Southern California, Hollywood's Cushion Track is the most similar to a dirt surface.\nSanta Margarita Invitational Handicap\nIn hindsight, Santa Teresita was a generous price when she upset the Santa Maria Handicap at 13-1 most recently. In one of those after the fact, "I should have had a V8" moments, it jumped off the page that Santa Teresita was switching from turf to a surface she clearly likes. Last year, she won a restricted stakes at Santa Anita off just such a surface switch, and later earned what was at the time a career-best Beyer finishing third in a four-horse race behind Zenyatta and Hystericalady in the Lady's Secret.\nSanta Teresita won't be 13-1 again Saturday, but she is the play to repeat. She figures to sit a sweet trip stalking a slow pace likely to be set by Forest Melody, giving her first jump on her main rivals, Life Is Sweet, Model, and Magical Fantasy.