Okoroba was fouled on his second layup in less than a minute after the Pirates (4-10, 2-0 Mid-Eastern Athletic Conference) had trailed 49-44 with 2:29 remaining.
Powers' free throw with 27 seconds left made it 51-49, but he missed his second try. After a missed shot by the Bison (4-13, 1-2), Du'Vaughn Maxwell couldn't put the game away, missing two free throws.
A steal by Powers with 4 seconds left denied Howard a final chance to tie or win.
Howard already had squandered plenty of chances, however, making just 9 of its 21 free throws. Hampton, which earned its first road victory this season, made 18 of 27.