Secretariat has won the virtual Kentucky Derby against 12 fellow Triple Crown winners, 47 years after the chestnut colt won the real race at Churchill Downs.

The 1-1/4-mile (2000m) race featuring computer-generated imagery was held on Saturday (Sunday AEST), the same day the 146th Derby had been scheduled until it was postponed by the coronavirus pandemic.

The Derby has been re-set for September 5.

Secretariat was the 7-2 favourite, although there was no wagering. Instead, fans selecting the winning horse online were entered to win a VIP experience at the rescheduled Derby.

Churchill Downs pledged to match $1 million in fan donations to COVID-19 relief.

Larry Collmus, who calls the Triple Crown races for NBC, provided a live call for the virtual Derby, seeing it unfold for the first time just as he would have been doing on the first Saturday in May.

"That was fun "calling" Secretariat and the other Triple Crown winners," he tweeted.

Seattle Slew, who won the 1977 Triple Crown, led much of the way until being overtaken in the straight.

Secretariat surged to the lead in the middle of the track to beat Citation and Seattle Slew.

Secretariat was a two-time Horse of the Year and swept the Derby, Preakness and Belmont, winning the last race by a record 31 lengths, in 1973.

Citation was the 1948 Triple Crown champion while Seattle Slew won the series in 1977

Affirmed (1978) , the 1978 champion, was fourth, followed by American Pharoah (2015).

NBC showed the real American Pharoah at Ashford Stud, where a flat-screen TV was set up in front of his stall to show the race.

Churchill Downs analysed the historical past performance of each Triple Crown winner and incorporated the opinions of horse racing experts who evaluated each contender's achievements and put them into historical perspective.

That information, known as the fundamental probabilities, was fed into Inspire Entertainment's computer models, which determined the final result by using those probabilities along with random number generation.

The fundamental probabilities only determined the chances of each horse winning. Those with a higher probability value were not necessarily going to win; they just had a greater chance of doing so.

Also in the race were 1946 champion Assault, Sir Barton (1919), Gallant Fox (1930), War Admiral (1937), champion Whirlaway (1941), Count Fleet (1943), Justify (2018) and Omaha (1935).

The virtual Derby was part of NBC's three-hour telecast that re-showed portions of the 2015 coverage when American Pharoah became the first Triple Crown champion in 37 years.

The show opened with Churchill Downs bugler Steve Buttleman playing "Call to the Post" from the front steps of his Louisville home. It moved to the track, with shots of empty stands, betting windows and the jockeys' room.

The track's stable area is set to re-open May 11, with live racing expected to resume on May 16.