LOUISVILLE, Ky. (AP) - Curlin will have to overcome 19 rivals and a lot of history if he is to win the Kentucky Derby.

The unbeaten colt was installed as the slight 7-2 favorite Wednesday after drawing the No. 2 post position. Affirmed was the last Derby winner to win from that post, and he went on to sweep the Triple Crown in 1978.

Winner of the Arkansas Derby for his third straight victory, Curlin will be ridden by Robby Albarado in a full field of 20 3-year-olds going 1 1/4 miles Saturday.

Curlin has two big things going against him: he didn't race as a 2-year-old and has run only three races in his career. It's been 125 years since Apollo won after skipping his 2-year-old season, and not since the filly Regret in 1915 has such a lightly seasoned horse worn the blanket of red roses.

Besides Curlin, trainer Steve Asmussen will saddle Zanjero, a 30-1 shot.

Tampa Bay Derby winner Street Sense was made the second choice at 4-1. Street Sense, last year's 2-year-old male horse of the year, will try to end the Juvenile jinx: no Breeders' Cup Juvenile winner has ever gone on to win the Derby, an 0-for-23 drought.

Street Sense, with Calvin Borel aboard, will leave from the No. 7 post for trainer Carl Nafzger, who won the 1990 Derby with Unbridled.

Churchill Downs oddsmaker Mike Battaglia said it was "very, very close" between Curlin and Street Sense, and he gave the nod to Asmussen's colt.

"He's undefeated," Battaglia said. "We don't know how good this horse is, but he's just been dominating."

Trainer Todd Pletcher will try to end his 0-for-14 skid in the Derby with a record-tying five entries: Any Given Saturday, Circular Quay, Cowtown Cat, Sam P. and Scat Daddy.

Circular Quay was made the 8-1 co-third choice, along with Nobiz Like Shobiz, trained by Barclay Tagg, who won in 2003 with Funny Cide. Circular Quay, who comes in off an eight-week layoff, will start in the No. 16 post. Wood Memorial winner Nobiz Like Shobiz will leave from the No. 12 post.

Florida Derby winner Scat Daddy was installed as the 10-1 fourth choice and will break from the No. 14 post.

Pletcher's other horses were not among the favorites. Any Given Saturday was listed at 12-1; Cowtown Cat and Sam P. were both 20-1.

While Pletcher has five entries, four other trainers have two horses in the field _ Asmussen has Curlin and Zanjero; Doug O'Neill has Great Hunter and Liquidity; Darrin Miller has Dominican and Sedgefield; and Bill Kaplan has Storm in May and Imawildandcrazyguy.

Since the 20-horse rule began in 1984, the race went off with the maximum field twice _ in 2005 when Giacomo won at 50-1 odds and last year when Barbaro won by 6 1/2 lengths.

Absent from this year's Derby will be three-time winning trainer Bob Baffert, who sent out three horses last year, and Hall of Fame trainers D. Wayne Lukas, a four-time winner, and Nick Zito, a two-time winner.