Per the below story they are testing Giacomo to be sure he didn\'t have a problem in the Belmont. If he wasn\'t one of the better horses to win the Derby its hard to see whats so shocking about his Belmont finish. Giacomo wasn\'t far off the pace and none of the pace horses were around at the end. That could be a function of the sealing and harrowing referred to here in earlier posts. (In other words, the track was certainly slower by the last dirt race and looks to have been slower during the Belmont Stakes.)
Giacomo was just outfinished by Chekov and A.P. Arrow, who both also ran close to the pace. Maybe those fractions were tiring.
http://www.drf.com/news/article/65937.html