Tensions mount as riders gear up for Kentucky Derby

(CNN) -- Nineteen horses and their riders geared up on Saturday for the nation's most celebrated horse race -- and first leg of the Triple Crown -- as an estimated 150,000 spectators gathered to watch the 137th edition of the Kentucky Derby at Churchill Downs.

The race, heralded as "the most exciting two minutes in sports," will feature America's premiere 3-year-old thoroughbreds, which will launch out of the starting gate in Louisville, Kentucky, at 6:24 p.m. ET.

The pack will then gallop around a 1.25-mile dirt course for a $2.17 million purse in what is the country's longest continuously running annual sports event.

The derby is the first leg of the Triple Crown, considered the most coveted achievement in thoroughbred racing. It is followed by the Preakness Stakes in Baltimore, Maryland, and the Belmont Stakes in Elmont, New York.

The last horse to win all three was "Affirmed" in 1978.

This year, racing aficionados have guardedly said that there is no clear front-runner.

"This derby on paper at least looks to be one of the most wide open derby's in recent memory," said Churchill Downs spokesman Darren Rogers.

Revelers in their famed derby hats began arriving at the track early Saturday, where 10 other races preceded the event.

"It's a tradition that was started years ago," Rogers said. "Everybody wears their favorite derby hat."

It's also a big day for gamblers.

Last year, officials tallied $21.5 million in on-track betting and $141.3 million in off-track betting for the Kentucky Derby alone.

More than 16.5 million viewers also tuned-in, the largest audience in 21 years.

Trying to make history is Anna "Rosie" Napravnik, who is looking to become the first ever female jockey to win the "Run for the Roses," as the Kentucky Derby is often referred.

Napravnik has pinned her hopes on a 20-1 colt named "Pants on Fire," and is only the sixth woman jockey in history to ride in the race.

The event's typical field of 20 hopefuls recently dropped to 19 when a horse named "Uncle Mo" was scratched from the race.

The once undefeated juvenile suffered a gastrointestinal infection after a third-place finish last month at Wood Memorial, according to race officials.

The remaining 19 horses are listed as follows:

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-- "Dialed In"

Trained by two-time Kentucky Derby winner Nick Zito, the Florida Derby winner drew post position eight. The thoroughbred was made an early 4-1 favorite. He will be ridden by Julien Leparoux, a French-born jockey who's flirted with success at Churchill Downs, but has yet to win the big race.

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-- "Twice the Appeal"

Trained by Jeff Bonde, Twice the Appeal cemented his spot at the Kentucky Derby with a victory at Sunland Derby on March 27. He stands at 20-1 odds and will break from post position three. His is ridden by famed jockey Calvin Borel, who has won three of the past four Kentucky Derbys.

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-- "Archarcharch"

Winner of the race at the Sugar Bowl at Fair Grounds, Archarcharch is trained by 70-year-old veteran William "Jinks" Fires and will be ridden by his son-in-law Jon Court. The colt was listed at 10-1 odds and will break from post position one.

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-- "Brilliant Speed"

Saturday's derby marks the horse's first race on dirt after a disappointing seventh-place finish in Saratoga. The colt -- who is trained by Tom Albertrani and ridden by Joel Rosario -- was listed as a 30-1 shot and will break from post position two.

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-- "Pants On Fire"

Winner of the Louisiana Derby in March, jockey Napravnik hopes to become the first woman to win the illustrious title. Her colt was listed at 20-1 odds.

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-- "Comma to the Top"

"Comma to the Top" will be ridden by jockey Patrick Valenzuela and come out of post position six. The colt, a 30-1 shot, enters the derby off a close loss in the Santa Anita Derby to Midnight Interlude, who is also a contender in Saturday's race.

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-- "Midnight Interlude"

Winner of the Santa Anita Derby, Midnight Interlude will be jockeyed by Victor Espinoza and was listed at 10-1. The colt will break from post position 15.

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-- "Mucho Macho Man"

The colt who placed third in the Louisiana Derby will be ridden by Rajiv Maragh in a 12-1 shot, breaking from post position 13.

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-- "Master of Hounds"

Ireland's own Aidan O'Brien trained the derby hopeful in his second trip to Churchill Downs. The horse is normally based in Ireland. The colt was listed at 13-1 odds.

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-- "Derby Kitten"

Ridden by Venezuela native Javier Castellano, "Derby Kitten" is trained by Mike Maker, who grew up outside of Detroit, Michigan. His jockey, Castellano, came to the U.S. in 1997, earning his biggest win at the Breeds' Cup Classic in 2004. The horse was listed at 34-1 odds.

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-- "Decisive Moment"

The colt, one of only two stakes winners in three generations of his female family, runs 37-1 odds. He is jockeyed by Kerwin Clark, a native of South Louisiana making his Kentucky Derby debut.

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-- "Twinspired"

"Twinspired" is jockeyed by Mike Smith, who followed in his father's chosen career and began racing at age 11. Smith won the Kentucky Derby in 2005 atop a horse named Giacomo. Meanwhile, "Twinspired" was listed at 29-1 odds.

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-- "Santiva"

Jockeyed by Jamaica native Shaun Bridgmohan, "Santiva" is reported to possess "strong stamina," and was listed at 35-1 odds. Bridgmohan, meanwhile, has recorded prior wins at Churchill Downsand, tallying more than 2,000 victories in his career.

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-- "Shackleford"

Jockeyed by Mexico City native Jesus Castanon, "Shackleford" was bred in Kentucky and trained by Dale Romans, who was raised near Churchill Downs. Romans has won more than 1,300 career races, with nearly a third of them occurring at the historic Kentury track. "Shackleford" was listed at 21-1 odds.

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-- "Animal Kingdom"

Jockeyed by derby veteran John Velazquez, "Animal Kingdom" was listed at 21-1 odds. Velazquez has ridden in 11 derby races, placing second in 2001.

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-- "Stay Thirsty"

Owned by Repole Stable, who once earned his money by way of the Glaceau company, which made the sport drinks "Vitaminwater" and "Smartwater," the colt was listed at 20-1 odds, having earned runner-up in the 2010 Grade I Hopeful Stakes.

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-- "Nehro"

Listed at 10-1 odds, Nehro will be ridden by Corey Nakatani and was trained by Steve Asmussen, a veteran trainer who earned 650 wins in 2009.

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-- "Watch Me Go"

A 30-1 shot trained by Kathleen O'Connell, "Watch Me Go" is jockeyed by Rafael Bejarano. The Peru native came to the United States in 2002, winning riding titles at every track in Kentucky.

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-- "Soldat"

A 14-1 shot, "Soldat" will be ridden by Alan Garcia, who is the last of three generations of professional riders from Peru. The horse was trained by Kiaran McLaughlin, who trained the 2006 Horse of the Year "Invasor."