No European-trained three-year-old has won the Group I Kentucky Derby, which will be run for the 144th time over 2000m on the main dirt track of Churchill Downs racecourse in Louisville, Kentucky, on Saturday.

But in the versatile colt Mendelssohn, O’Brien may well have the joker in the pack of 20 runners.

Some six hours after the Kentucky extravaganza that is promoted as America’s greatest two minutes of sport has been decided, and across the Atlantic at historic Newmarket racecourse in England, O’Brien will bid to have his name on the 2000 Guineas roll of honour for a ninth time.

From a breeding standpoint, the Kentucky Derby-2000 Guineas double was achieved in 2006 by US residents Roy and Gretchen Jackson, who bred and raced the Derby winner Barbaro and bred and sold the 2000 Guineas winner George Washington (the latest of O’Brien’s eight winners).

O’Brien has a platoon of nominations for the 2000 Guineas, but the task will be handed to two principals, the Galileo colt Gustav Klimt, a firm favourite for this classic, and the Deep Impact colt Saxon Warrior, who is one of three equal-second-favourites for Saturday and who heads the markets for the Group I English Derby in June.

Since being appointed in 1996 as private trainer for Coolmore Stud’s racing operation, O’Brien has set the record books for world flat racing on fire — his achievements placing him furlongs ahead of the field.

Just one statistic is required to flag O’Brien’s influence — he has won 299 Group I races around the world: 94 in his native Ireland, 131 in England, 42 in France, 23 in the US, three in Italy, two in Canada and Hong Kong and one each in the United Arab Emirates and Australia (Adelaide in the 2014 Cox Plate).

Mendelssohn already figures on O’Brien’s dizzy tally of Group I winners, having travelled from his Ireland base in November to the US where he won the $US1 million Breeders’ Cup Juvenile Turf.

But it was Mendelssohn’s staggering performance in the Group II $US2m UAE Derby at Dubai’s World Cup meeting in late March that earned the colt a ticket to Churchill Downs — and as the first in line to bid for O’Brien’s 300th Group I triumph.

Already a winner on grass and on a synthetic surface in Ireland, Mendelssohn took to Meydan’s dirt track as a natural, freewheeling in front early in the 1900m set-weight UAE Derby then rolling on to win by 18½ lengths in track record time.

Mendelssohn was born to run on dirt, bred as he was in Kentucky on May 17, 2015, which has him still a two-year-old by actual birthdate. He went to the Keeneland sale ring in September 2016, where he was bought by Coolmore as the $US3m sale’s topper and the year’s most expensive yearling anywhere.

Mendelssohn is by the short-lived stud phenomenon Scat Daddy, a great grandson of multiple US leading sire Storm Cat.

The horse’s mother Leslie’s Lady, an honest runner in restricted company, is from a workmanlike family of regular winners. But she herself has lifted the family profile substantially as the dam of multi-award-winning mare Beholder, the highly commercial stallion Into Mischief and now the prime Kentucky Derby candidate Mendelssohn.

Leslie’s Lady, who is now aged 22, gave birth on April 25 to a filly by the celebrated 2015 Triple Crown winner American Pharoah, who will be shuttling to Coolmore’s NSW Hunter Valley property for the second time this spring.

She also has a yearling colt scheduled for the Keeneland sale ring in September — this one by Darley Stud’s Medaglia d’Oro, who is a scratching from this year’s shuttle after eight consecutive seasons in the Hunter Valley.

Fourth in War Emblem’s 2002 Kentucky Derby, Medaglia d’Oro has Bolt d’Oro, a one-time favourite, and the Godolphin colt Enticed, poised to run on Saturday.

A dual Group I winner at two years, Bolt d’Oro was runner-up in the recent Group I Santa Anita Derby while Enticed has performed well in two traditional Derby lead-ups, winning the Group III Gotham Stakes followed by a second in the Group II Wood Memorial.

A $US630,000 yearling and named for Olympic sprint champion Usain Bolt, Bolt d’Oro is owned by his hobby trainer Mick Ruis, a remarkable individual who worked from the basement to develop a scaffolding business, 80 per cent of which he sold in 2016 for $US78m.

International big spender the China Horse Club and Kentucky’s Winstar Farm are involved in the ownership of two leading Derby candidates, the unbeaten Santa Anita Derby winner Justify and the Group I Florida Derby winner Audible — from the big league stables of Bob Baffert and Todd Pletcher, respectively.

Audible, a $US500,000 breeze-up sale buy as an unraced two-year-old, is by Mendelssohn’s half-brother Into Mischief, while Justify is another top notch performer by Scat Daddy and who fetched $US500,000 at the same sale where Mendelssohn was bought.

Justify is the ruling Kentucky Derby favourite after three unbeaten starts, stepping into stakes company for the first time in the Santa Anita Derby where he was hugely impressive in front and drawing away by three lengths at the finish.

A vital question asked of Justify is that not having competed against more than six rivals in his three outings, how will he fare with the hustle and bustle of a 20-strong Derby field for which several hopefuls have shown to be natural frontrunners?

And another question is how will he address the bogey that has played out since Apollo in 1882 — the last Derby winner not to have raced as a two-year-old?

That bogey not only applies this time to Justify but also to Magnum Moon, which made the Group I Arkansas Derby his fourth unbeaten start since a January debut.

By Malibu Moon, sire of 2013 Derby winner Orb, Magnum Moon is another from the Pletcher stable.

The Apollo bogey found out Curlin, third in the 2007 Derby, before he won almost everything in his path to eventually retire as the first $US10m stakes winner in US racing.

By premier sire Smart Strike, Curlin has three representatives heading for Churchill Downs — the recent Group II Blue Grass Stakes winner Good Magic, Group II Wood Memorial winner Vin Rosso and the Arkansas Derby third Solomini, who runs for the American Pharoah team of owner Zayat Stables and trainer Baffert.

Australia had a strong Kentucky Derby interest up until early last week with the British-trained Gronkowski, a US-bred son of Darley Stud’s champion sire Lonhro, who shuttled for two seasons to Kentucky.

Having qualified for the Kentucky Derby by winning a trial race on a synthetic surface in ­England, Gronkowski was withdrawn after being treated with antibiotics for a temperature spike — which ruled him out of travelling the Atlantic.

Like Mendelssohn, a winner on grass, dirt and synthetic tracks, Gronkowski may still visit the US with connections planning a crack at the Group I Belmont Stakes, third leg of the US triple crown, in New York in June.

Here is a look at the final order and race times (lengths behind) for Justify and the entire field from Saturday's race at Churchill Downs in Louisville, Kentucky, per NBC's broadcast:

Win ($1.24 million): Justify; Jockey: Mike Smith; Trainer: Bob Baffert

Place ($400,000): Good Magic (-2 ½ lengths); Jockey: Jose Ortiz; Trainer: Chad Brown

Show ($200,000): Audible (-2 ½ lengths); Jockey: Javier Castellano; Trainer: Todd Pletcher

4th ($100,000): Instilled Regard (-4 ¼ lengths); Jockey: Drayden Van Dyke; Trainer: Jerry Hollendorfer

5th ($60,000): My Boy Jack (-7 lengths); Jockey: Kent Desormeaux; Trainer: J. Keith Desormeaux

6th: Bravazo (-8 lengths); Jockey: Luis Contreras; Trainer: D. Wayne Lukas

7th: Hofburg (-8 ¾ lengths); Jockey: Irad Ortiz Jr.; Trainer: William Mott

8th: Lone Sailor (-9 ¼ lengths); Jockey: James Graham; Trainer: Thomas Amoss

9th: Vino Rosso (-10 ½ lengths); Jockey: John Velazquez; Trainer: Todd Pletcher

10th: Solomini (-11 lengths); Jockey: Flavien Prat; Trainer: Bob Baffert

11th: Firenze Fire (-23 ½ lengths); Jockey: Paco Lopez; Trainer: Jason Servis

12th: Bolt d'Oro (-24 ¼ lengths); Jockey: Victor Espinoza; Trainer: Mick Ruis

13th: Flameaway (-30 ½ lengths); Jockey: Jose Lezcano; Trainer: Mark Casse

14th: Enticed (-34 ¾ lengths); Jockey: Junior Alvarado; Trainer: Kiaran McLaughlin

15th: Promises Fulfilled (-39 ¾ lengths); Jockey: Corey Lanerie; Trainer: Dale Romans

16th: Free Drop Billy (-41 lengths); Jockey: Robby Albarado; Trainer: Dale Romans

17th: Noble Indy (-42 ¼ lengths); Jockey: Florent Geroux; Trainer: Todd Pletcher

18th: Combatant (-42 ¾ lengths); Jockey: Ricardo Santana Jr.; Trainer: Steven Asmussen

19th: Magnum Moon (-49 ½ lengths); Jockey: Luis Saez; Trainer: Todd Pletcher

20th: Mendelssohn (-73 ¼ lengths); Jockey: Ryan Moore; Trainer: Aidan O'Brien