Netherlands' Pieter van den Hoogenband stormed home on the final length to claim his second Olympic gold medal at these Games.
He posted a time of 48.30 to hold off Russia's defending Olympic champion Alexander Popov by almost two-fifths of a second (0.40).
After breaking a split world record in the 4×100 m freestyle relay on the opening night, Australia's overwhelming favorite Michael Klim missed out the podium in a close race against Hall by a hundredth of a second, finishing with a time of 48.74.
[6] Klim was followed in fifth by Hall's teammate Neil Walker (49.09), and in sixth by Sweden's three-time Olympian Lars Frölander (49.22).
Two other swimmers, Niger's Karim Bare and Tajikistan's Farkhod Oripov, plunged into the pool and were cast out of the race under a no false-start rule, leaving Moussambani as the last man standing.
Cheered by a large crowd, he finished a one-man heat in 1:52.72, nearly seven seconds slower than a winning time by Van den Hoogenband over double the distance a day before.