Updated: May 6, 9:11 a.m.

At the start of the year, people involved in thoroughbred racing were speculating whether Uncle Mo would win the Kentucky Derby and go on to sweep the Triple Crown series. Three weeks ago they were asking if he would be fit and healthy enough to perform well in the Derby. This week they were wondering if he would even get to the starting gate. Friday morning, they got the disappointing answer: The colt will be scratched from Saturday’s race.

In a way, the decision by trainer Todd Pletcher and owner Mike Repole shouldn’t affect bettors’ analysis of the Derby. There were so many negative signs surrounding Uncle Mo that many handicappers were prepared to throw him out — even though he was, on his best form the oustanding horse in the field.

After his championship season as a 2-year-old, Uncle Mo’s 3-year-old campaign has gone awry from the start. He won a trumped-up race at Gulfstream Park that was little more than a glorified workout and then suffered a shocking loss against a terrible field in the Wood Memorial Stakes. A few days later Pletcher issued a press release saying that Uncle Mo was found to be suffering from a gastrointestinal infection—the excuse for the defeat.

Some skeptics weren’t fully satisfied with this explanation, because owners and trainers rarely tell the whole truth about horses’ physical problems. Questions about Uncle Mo multiplied since he arrived at Churchill Downs. His two workouts were undefinitive. His camp kept hedging about whether he would run. Repole announced that he, Pletcher and three veterinarians would confer Thursday evening to decide the colt’s status — hardly a sign of confidence two days before the Derby.

With Uncle Mo out of the lineup, Florida Derby winner Dialed In solidifed his status as the favorite. Many fans have watched his exciting last-to-first rallies and concluded that Nick Zito’s colt is a natural Derby horse.

Yes, Dialed In was impressive charging from far behind to win the one-mile Holy Bull Stakes at Gulfstream in January. But in his two subsequent starts at 11 / 8 miles, he lost an allowance race and then struggled to win the Florida Derby. The race — filled with speed horses, run with fast early fractions — was a perfect setup for him, yet Dialed In barely got past the 68-to-1 pacesetter, Shackleford, to prevail in slow time. Eleven horses in the Kentucky Derby field have earned higher Beyer Speed Figures in 11 / 8-mile race than Dialed In did in either of his starts at the distance. I believe that Dialed In’s best game is rallying at shorter distances, and that he will be even less effective at 1¼ miles. Throw him out.

None of the Derby entrants (except for Uncle Mo) has yet run a race good enough to stamp himself clearly as a potential Derby winner. Their speed figures are all sub-par. In these circumstances, it makes sense to look for a colt whose form is on the upgrade and is likely to improve further on Saturday. Based on this standard, these are my top three:

1. Shackleford

2. Archarcharch

3. Nehro

While Dialed In received acclaim for his come-from-behind Florida Derby victory, Shackleford gave a superior performance in defeat. He outsprinted several formidable speedsters, set a fast pace and refused to yield when Dialed In hooked him. This race represented an improvement over his four previous starts, and he may still be improving — as indicated by his fast five-furlong workout in 58.83 seconds at Churchill Downs. Is he a 11 / 4-mile horse? Maybe not. But at healthy odds I’ll take the chance that his sharp form will trump any of his shortcomings.

Archarcharch and Nehro finished 1-2 in the competitive 13-horse Arkansas Derby, with Archarcharch rallying past the tired leaders to take command and Nehro unleashing a powerful late run to miss by a neck. Both have raced four times at a mile or more since mid-January; they’re fit. Both have solid pedigrees for 11 / 4 miles. Both are improving; they delivered the best races of their lives in the Arkansas Derby. Archarcharch is training especially well; after he worked five furlongs in 59.31 seconds last week, clocker Bruno De Julio wrote at “He is a serious racehorse hitting his stride.” If a hot early pace in the Derby takes a toll on the leaders — a common scenario at Churchill Downs — Archarcharch and Nehro are the stretch-runners most likely to capitalize.

Because a handicapper has to bet horses on the basis of hoped-for improvement rather than actual accomplishments, this is an especially challenging Kentucky Derby. But the potential for giant payoffs makes the race irresistible. My plan is to box my Shackleford, Archarcharch and Nehro in the exacta, and then to use them on top in trifecta and superfecta combinations that will not include Dialed In — and would not have included Uncle Mo if he had stayed in the race.