Secretariat lost five races - one of them on a disqualification. He had an excuse in the Wood with the abscess, but he was just outrun by the two Jerkins' horses in the Whitney and Woodward - it happens.
Forget the sloppy track excuse - Secretariat was fine on an off-track. Meadow Stable entered two horses in the Woodward...they would run Riva Ridge if it was a fast track and Secretariat if it rained. It rained, so Secretariat got the call. (Kind of a luxury - Meadow Stable had the '72 and '73 Derby winners in their barn.)
Prove Out, the horse that outran Secretariat in the Woodward, was hardly a plug - when he was healthy, he was a pure freak. He had a brilliant stretch that fall that saw him set a track record at seven furlongs at Saratoga while smoking Forego, set another track record at 1 1/16th at Belmont and then he beat Secretariat at a mile and a half and Riva Ridge at two miles. The 2:25 4/5ths winning time of the Woodward is still the second-fastest mile and a half ever run at Belmont.