Ladies and Gentlemen: the Kentucky Derby. Back when the earth was still hoary and the sky gray, we looked to Florida, to Arkansas, to California, and occasionally to icy Aqueduct to watch a young crop of colts begin the march toward the first Saturday in May. They were young and unpredictable, and we were straining to see if they would live up to or exceed their juvenile reputations, or if they would, like so many prodigies, disappoint as maturity neared. In each case, the jury remains out.

The most heavily raced horse in the gate Saturday has only five starts as a 3-year-old, and most have only three. They have battled in sectional prep races against a few rivals, and only the best of those have made their way to the Kentucky Derby, where we will find out what they are truly made of. This is the race that divides a generation of colts and turns hunches into facts. There are no second acts in the Kentucky Derby. The greatest two minutes in sports is a sea change for 3-year-old thoroughbreds, and indeed, one of them will transform into something rich and strange.

Just as the moment of change is upon a strong field of 20 3-year-old colts, it seems that this Derby, more than any other, heralds a change in the sport itself. Of course that’s not the way things work, it’s always a gradual process. But a look at the field puts a new relief on racing.

Consider this: Of the 10 trainers with the most Derby starters in history, three are still running horses: Bob Baffert, Nick Zito, and D. Wayne Lukas. Together, those three have sent 78 horses to the gate. Scan the sheets in vain, but none of them is here this year. Neither is Bobby Frankel nor Bill Mott, nor any of the other trainers we’ve come to think of as fixtures on big stakes days. Try this one: Although I’m sure that more than a few will be in the box seats tomorrow, there isn’t a hall of fame trainer with a horse in this race.

New trainers bring new styles, and with each passing year, it seems a few more of our old theories on what makes a horse a Derby horse get shattered. Prejudice and traditionalism have long held sway in Kentucky, and bets have long been made accordingly. Remember when New-York-bred geldings weren’t supposed to win the Derby? Funny Cide. Remember when you couldn’t win the Derby with a long layoff? Barbaro. Remember when people didn’t think so highly about the races in Arkansas? Smarty Jones. Remember when your horse had to have won a couple of races? Giacomo. The last few years have been tough on traditions and prejudice.

This seems to have been taken to heart, with most of the field poised to crack one or another long-held belief about how one wins the roses.

Last year, Barbaro’s trainer, Michael Matz, had to answer an endless barrage of questions about bringing his horse into the Derby off a five-week layoff. Barbaro proceeded to a thrilling victory. This year, Circular Quay is coming in off an eight-week layoff, Hard Spun hasn’t raced in six weeks, and both Scat Daddy and Imawildandcrazyguy last raced in the Florida Derby, five weeks ago.

Another long-held belief is that you must have three preps coming into the race. Street Sense, Circular Quay, Great Hunter, Stormello, and Dominican each have two.

Tomorrow’s Morning Line favorite, Curlin, meets the above requirements, but has only three starts total and did not race at all as a 2-year-old.

Here is the wisdom that has been handed down about which horse should win the Derby: The horse must have started at age 2 and had three prep races at 3, at least two of which were around two turns. The horse must have raced within four weeks of the Derby and finished third or better. Lastly, the horse must have earned at least one triple-digit Beyer Speed Figure at age 3. If we take into account all the so-called rules accepted as prerequisites, only two horses among the 20 meet the criteria: Tiago and Any Given Saturday. Of those two, only Tiago has won a Grade 1 race, having been impressively piloted by Mike Smith to win the Santa Anita Derby.

If you’re looking for a good reason not to eat chalk, there it is.

The Derby is awash in tradition: Early Times Mint Juleps and seersucker suits, “My Old Kentucky Home” and extravagant hats, mud-wrestling in the infield and those plastic riot handcuffs. But perhaps it’s time to let them go. Just as we must accept the order of finish once the “official” sign lights up on the board, we must accept change as it comes. These are different times, and we should use different criteria to judge where we lay our money.

Of course if Tiago comes romping home, don’t say I didn’t warn you.

mwatman@nysun.com