South Alabama (2-2) trailed 70-66 before Augustine Rubit made a layup, then three free throws to give the Jaguars a 71-70 lead with six seconds left.
Steele, with one second left, got fouled by Antoine Allen while shooting a 3-pointer. Steele made all three free throws to give Monmouth (2-3) the win.
Andrew Nicholas led three Hawk players in double-digits with 15 points.
Dion Nesmith scored 12 points for Monmouth, while Steele came off the bench to finish with 11 points, eight assist and four steals.
Marcus Ware chipped in 13 points off the bench and eight rebounds.
Rubit finished with a double-double, 20 points and 16 rebounds, to go along with five blocks.