LOUISVILLE, Ky. — All week, the chatter along the Churchill Downs backstretch has been about Big Brown running away with the Kentucky Derby.

The talk ends Saturday and the real running begins in 1 1/4-mile Derby, where the unbeaten 3-year-old colt has plenty to prove, history to buck and perhaps even a wet track to overcome.

Big Brown is the 3-1 morning-line favorite in a full 20-horse field that includes Santa Anita Derby winner Colonel John and Eight Belles, who will try to become the fourth filly to win the Run for the Roses.

Toss in Louisiana Derby winner Pyro, Blue Grass winner Monba, Wood Memorial winner Tale of Ekati and Arkansas Derby winner Gayego, and the race could be more wide-open than many expect.

"His favoritism is clear," Derby oddsmaker Mike Battaglia says, referring to Big Brown. "But is it really clear he's that good?"

So far, Big Brown has looked the part of a champion, and trainer Rick Dutrow Jr. has voiced his confidence in the 3-year-old colt for more than a month. The Florida Derby winner has won all three of his races by a combined 29 lengths.

"I feel we have the best horse in the race, the fastest horse," Dutrow said Friday morning outside his barn. "He's giving me every indication that he is sitting on a big race."

Another dominant win by Big Brown would renew hopes that there could be a Triple Crown champion for the first time since Affirmed swept the Derby, Preakness and Belmont Stakes in 1978.

Colonel John, the 4-1 second choice, has never been worse than second in six career starts — all on synthetic tracks made of wax-coated sand, fibers and recycled rubber.

That raises the second-most compelling question in this Derby: Can he make the transition to dirt?

"I've liked what I've seen since I got here and I have no reason to change my opinion," trainer Eoin Harty said.

And what about the filly Eight Belles, 4-for-4 this year, taking on the boys for the first time? It's been nine years since a filly ran in the Derby, with Winning Colors the last to win it in 1988.

"We think she belongs," Eight Belles owner Rick Porter said. "Right now, you don't know how good Big Brown is."

While Big Brown might be the one to beat, favorites don't often come through. Only three favorites have won since Spectacular Bid in 1979, including Street Sense last year. Giacomo, at 50-1 odds, won in 2005.

Overnight thunderstorms could leave the racing strip a mess Saturday. Weather.com called for the storms to end early Saturday, with a 20 percent chance of rain and temperatures in the low 70s by the Derby post time of 6:04 p.m.

A wet track could be good news for a bunch of Derby long shots. Cool Coal Man, Visionaire, Smooth Air and Denis of Cork have won over sloppy tracks. Pyro ran second in the Breeders' Cup Juvenile at muddy Monmouth Park. Tale of Ekati, Big Truck and Z Humor hate the mud.

There's a bit of Derby history being challenged, too.

Big Brown and Colonel John, for example, are among six horses with just two preps this year. The others are Court Vision, Monba, Tale of Ekati and Recapturetheglory. Since 1947, only Sunny's Halo in 1983 and Street Sense have won the Derby off two preps. Big Brown is also looking at this: The last Derby winner with three career starts was the filly Regret in 1915.

Nine of the 20 horses are coming off synthetic surfaces, and like Colonel John, Big Black Jack will be running on dirt for the first time.

Pyro, a one-time Derby favorite, finished 10th in the Blue Grass on Polytrack at Keeneland, the colt's first race off the dirt. Pyro, trained by Steve Asmussen, looks to rebound as the 6-1 third choice.

Two other Derby horses, Cool Coal Man and Big Truck, ran poorly in the Blue Grass.

Meanwhile, Monba and Cowboy Cal ran 1-2 in the race to give trainer Todd Pletcher a chance at ending his 0-for-19 record in the Derby.

Gayego, a 15-1 choice, raced exclusively on synthetic surfaces, but won the Arkansas Derby on the dirt in his last start.

Big Brown's fate could be decided at the start. A clean break and fast start are imperative for a horse on the far outside. Since 1900, the only Derby winner from the No. 20 post was Clyde Van Dusen in 1929.

"It might be too far out there, but we were willing to accept that challenge," Dutrow said. "He usually breaks good. He usually puts himself right in the game."

Bob Black Jack, who starts from the No. 13 post, may be the only horse who can match the speed of Big Brown, having set a world record for six furlongs (1:06.53) in winning the Sunshine Millions Dash at Santa Anita. Others expected to contest the early lead are Cowboy Cal and Recapturetheglory.

"When the doors open," Desormeaux said, "I'm going to feel it. I don't know where I'm going to be. It's just one of those things. If they let me, I can lead the parade around there."

If the leaders tire in the stretch of the longest race any of these horses have run, look for closers such as Court Vision, Pyro and Visionaire to be running strong at the end.

The Derby is worth $2,211,800, with the winner earning $1,451,800.

Dutrow and Harty are among six trainers in their first Derby. The others are: David Carroll (Denis of Cork), James Kasparoff (Bob Black Jack), Paulo Lobo (Gayego) and Bennie Stutts (Smooth Air).

Pletcher is one of five trainers with two horses in the field. The others are: Barclay Tagg (Big Truck, Tale of Ekati); Bill Mott (Court Vision, Z Humor); Asmussen (Pyro, Z Fortune); and Nick Zito (Anak Nakal, Cool Coal Man).

Last year, Curlin came into the Derby with a profile similar to Big Brown's, and finished third. The colt went on to take the Preakness and the Breeders' Cup Classic to earn Horse of the Year honors, and won the Dubai World Cup in March.

Perfection is hard to maintain in the Derby. Two years ago, Barbaro became just the sixth unbeaten Derby winner.

"I'm sitting on go here," Dutrow said. "We're ready."