Kentucky Derby entrant Uncle Mo with exercise rider Hector Ramos worksout during morning preparations for the 137th running of the Kentucky Derby. (Jamie Squire/GETTY IMAGES)

When 19 horses charge from the gate Saturday in the 137th running of the Kentucky Derby, it will mark the start of what — even in a down year — can still be called the two most exciting minutes in all of sports.

But the reality of the 2011 Derby is the horse that isn’t in the race might be a bigger story than the ones that are.

That could change, of course. The winner might emerge as a star, a horse capable of winning the Preakness Stakes in two weeks and competing for the Belmont in June, and give a niche sport some much-needed buzz. But that could also be wishful thinking. When Uncle Mo was scratched on Friday morning with a mysterious internal illness, it marked the third straight year the most talented horse in the field didn’t make it to the starting gate.

In 2009, I Want Revenge and Quality Road failed to run because of injury. Eskendereya had to be scratched in 2010. And now Uncle Mo this year.

Uncle Mo wasn’t quite the morning-line favorite this year. That honor went to Dialed In, a lightly-raced Nick Zito-trained colt who won the Florida Derby. But virtually everyone acknowledges that if Uncle Mo were healthy, he’d likely be the horse to beat.

“He’s a very, very special horse,” said Todd Pletcher, who won his first Derby last year. “If he’s right, you come into a race feeling very confident.”

Uncle Mo hasn’t looked right, however, ever since he finished third at the Wood Memorial in early April. His absence is another blow to a sport that can’t seem to keep some of its best athletes healthy.

“I am very, very, very, very disappointed about this,” Pletcher said. “I don’t think I’ve ever had a horse as good as Uncle Mo. We’ve had every resource to try to get this horse right, but we’re not there. I take it as a personal failure. We just don’t know what’s wrong with this horse, and it scares me.”

Even Zito, who will be trying to win his third Kentucky Derby Saturday and could benefit significantly from Uncle Mo’s absence, was quick to acknowledge what a bad break it was for horse racing.

“I am disappointed, like everyone else,” Zito said. “He is a great horse and I feel sorry for the connections. It’s a tough business we are in right now. I just would have loved to have seen Uncle Mo win the Wood and go onto the Derby. There would have been a lot of hype for the horse and the game needs that. It’s unfortunate and it will happen again, which is also unfortunate. It just goes to show you that it’s a very tough thing to get to the Kentucky Derby.”

Even this year, Uncle Mo wasn’t the only serious contender bounced from the field. Maryland-based trainer Graham Motion lost a promising starter in Toby’s Corner before the week had barely begun. Toby’s Corner won the Wood Memorial when Uncle Mo tired.

“It’s been a real emotional roller coaster for everybody, particularly for the guys at Fair Hill, who put so much into Toby’s Corner,” Motion said. “But that is the nature of the game and it’s what you grow used to.”

There will be a winner, of course, but who it might be is shaping up to be one of the toughest calls in years. Dialed In looks like a safe bet to hit the board, but he’s a closer without a lot of early speed, and asking him to weave through traffic and run the perfect race is a lot from a horse that’s only run four times in his career. And Zito knows as well as anyone that having the best horse at the Derby is no guarantee for success. Last year, he might have won his third Derby with Ice Box had the horse not run into traffic multiple times in pursuit of Super Saver.

“I love my horse,” Zito said. “He is a well deserving morning-line favorite and I hope everything works out. . . . It’s been a long time since we’ve won this race, but you’ve got to be thankful for the ones you’ve won.”

In the absence of a dominant performer, a big group of owners and trainers feel they have a legitimate shot at snatching the blanket of roses awarded to the winner. Even long shot Twice the Appeal, who began the week at 30-1 odds, was drawing heavy action early for reasons that can only be explained by his jockey, Calvin Borel, who will be trying to win his third straight Derby and his fourth in five years.

“I’m going to have my wife bet $500 on Calvin Borel, just in case,” said trainer Bob Baffert, who has his own long shot, Midnight Interlude, in the race. “If it’s wet, he’ll ride that rail and he’s good for seven or eight lengths.”

Realistically, Borel may not have enough horse underneath him this year to pull off the three-peat. Twice the Appeal has just three wins in 10 career starts. But the Louisville forecast is calling for rain showers in the afternoon, and on a muddy track, anything can happen.

If you’re looking for a sentimental favorite with a legitimate chance, you can’t do much better than Mucho Macho Man. He nearly died as a foal before springing to life right when veterinarians were about to give up on him. Even better, his trainer, Kathy Ritvo, had a heart transplant three years ago.

“It’s not a high pressure week for me,” Ritvo said. “The high pressure week for me was waiting for a heart. This is fun.”

If you like bucking historical trends, Archarcharch is a compelling pick. The Arkansas Derby winner has trained better than every horse at Churchill Downs this week, and has a veteran trainer in Jinks Fires. But the horse’s chances took a serious hit at the post position draw when he drew the No. 1 spot. The last horse to win the Derby in a field of 17 or more who started on the rail was War Admiral in 1937. Jockey Jon Court will need to fall back from the pack and stage a late charge to buck that trend.

Nehro is another legitimate contender who is hampered by an unfortunate post position. He drew No. 19, a spot no horse has ever won from, although when Uncle Mo was scratched, it did mean he could slide down one stall. A runner-up in the Arkansas Derby and the Louisiana Derby, Nehro has shown rapid improvement in recent months, and may be peaking at the right time.

But with rain looming and no dominant horse in the field, maybe it will be the kind of year where a horse like Mine That Bird — who prior to the race was a 50-1 long shot — stuns everyone with a surprise victory.

“I think about 10 horses have a chance to win,” Baffert said.

It’s just a shame, for the sake of the sport, Uncle Mo isn’t one of them.

— Baltimore Sun