I can understand your doubt - but, I assure you that it is entirely true.
I was amazed at how hard he pushed himself; he went all out. He was virtually carried away from the finish line.
The next night I went to the fight. He fought Iron Jaw Pravda. Iron Jaw was an apt name, because Sugar Ray he him so hard it was frightening, yet Iron Jaw never went down. (Later in the year, Sugar Ray knocked out Tommy "the hit man" Hearns.)
Sugar Ray was a young idealist. When he fought Roberto Duran the first time, he fought Duran in Duran's style just out of sportsmanship. Duran won on points, but went on to humiliate/embarass Sugar Ray in the post fight activities. Sugar Ray took it personal and the next time they fought, he made Duran look silly (admittedly Duran was past his prime) and Duran quit in the infamous "no mas" fight.
But, back to the race, yes, it happened all right, just as I described.