Drawing a favorable post and benefiting from a late scratch by one of his top threats, American Pharoah will enter Saturday’s Breeders Cup Classic as a heavy 4/5 favorite to claim horse racing’s first-ever grand slam at Keeneland in Lexington, Kentucky.

The three-year-old bay-colored colt stands well above the now nine-thoroughbred field with his odds improving from 13/10 last week to 4/5 after he drew the No. 4 post when the positions were announced Tuesday for the 1 1/4-mile contest.

American Pharoah and his connections, owner Zayat Stables and trainer Bob Baffert, saw their official odds jump after contender Beholder was scratched Thursday. According to Daily Racing Form, Beholder’s trainer Richard Mandella noticed the horse’s temperature was raised by one degree earlier this week, and after carefully monitoring and testing the five-year-old mare during workouts over the course of several days he noticed some blood in the horse’s trachea and learned it was an irritation in her lungs.

Prior to the late scratch, Beholder was seen as American Pharoah’s main competition at 3/1 odds last week.

Her omission has allowed Tonalist to shift up from 6/1 to 4/1 odds, but the 2014 Belmont victor will have to work out of the No. 1 post and could get pinned inside out of the gate.

However, Tonalist’s chances are viewed as only slightly better than Honor Code, who will try to work his way into the middle of the pack from the No. 9 post. The four-year-old colt, who counts Triple Crown-winner Seattle Slew as part of his lineage, has won six of his 10 career races and even bested Tonalist at the Grade 1 Metropolitan at Belmar back in June.

Having already claimed the Kentucky Derby, Preakness Stakes, and Belmont Stakes earlier this year for the first Triple Crown in 37 years, American Pharoah and jockey Victor Espinoza aim for one more slice of racing history.

The Breeders Cup Classic first began in 1984, meaning previous Triple Crown-winners before American Pharoah haven’t had a shot at claiming all four of the sports’ major stakes races. Affirmed was the last to claim the Triple Crown, back in 1978, six years before the Classic’s inception.

With a total purse of $5 million, $2.75 million of which going to the winner, the Classic is the richest race held in the U.S. and a victory for American Pharoah could reap huge benefits for his connections.

Posts, Odds To Win Breeders Cup Classic

1.Tonalist 4/1

2.Keen Ice 8/1

3.Frosted 12/1

4.American Pharoah 4/5

5.Gleneagles 20/1

6.Effinex 20/1

7.Smooth Roller 12/1

8.Hard Aces 30/1

9.Honor Code 5/1