Certainly of the modern era. Given that Secretariat set a track record in that race (which I believe still stands) while not being pressured in the least, it makes you wonder what kind of time he might have posted if pushed.
This situation reminds me of the situation with Spectatular Bid in 1979 when it was debated whether to run him in the Belmont or not due to injury. Although injured, it was decided to run him. He lost to some horses that he had already clearly established he could beat easily when healthy.
Of all the horses in that time frame, I've always thought that Spectacular Bid was the horse that would have most challenged Secretariat. More so than Affirmed or Seattle Slew or Alydar.
Secretariat was the greatest race horse that ever lived. He won the Derby, Preakness and Belmont in record time and the Belmont by 31 lengths. No horse has even come close to that performance. Get the movie—great story that you can watch over and over.
Bid stepped on a safety pin the morning of the Belmont. It was the day after my HS graduation.
This now 35-year (by next year) TC drought ought to be called the Safety Pin Jinx.