Nelson, a former England international guard, was released to make room under the salary cap for Tigers to re-sign former player Tony Balogun.
Steve Bucknall gave Tigers an 84-83 lead with two minutes to play, before Bears' player-coach Alan Cunningham edged Worthing in front with two free throws.
Then the 6ft 4in Nelson, who had scored just three points, added two quick baskets before three more points from Cunningham and two points from Colin Irish.
Out-scored 11-0 in under two minutes, a late basket from Peter Scantlebury could not save Tigers from their sixth League defeat of the season in front of a record 1,500 crowd in Worthing's refurbished Arena.
No club has ever won the League after losing more than five games, and Tigers lost further ground to the leaders with Sheffield beating Hemel Royals 95-59 to go 10 points clear at the top.
Second placed London Towers, who have also lost six matches, condemned third-placed Manchester to their seventh defeat with an 89-84 win at the Giants.
Manchester led 77-70 but lost their poise after an intentional foul was called on Trevor Gordon, spurring London to score the next seven points. Ken Scott scored 30 points for London.