Johnville Renee’s goal just before the break was enough to give Blues a share of the points at King George’s Fields, on Saturday.
But Renee levelled on the stroke of half-time when he rose above the home defence to powerfully head home.
The rest of the first had resembled a typical end-of-season game despite Casuals needing a win to pull away from the bottom three.
Luke Callandar became the first Stortford player to go into referee Craig Green’s notebook shortly after the break before being immediately replaced by Olly Miles and Jack Thomas also picked up a yellow card before Charles joined the action in place of George Craddock.
Ryan Henshaw kept Blues on level terms in the 67th minute when he hooked the ball off the line after Benjamin Aghadiuno had beaten Arthur Janata in the visitors’ goal.
Janata did well to deny Aghadiuno late in the game, but the final minute of normal time saw Adam Bailey-Dennis’ return to the Blues end with a red card as he was harshly dismissed for what appeared to be a clean tackle on Aghadiuno.
The visitors held on in injury time with Janata bringing off a fine save from Jack Strange to give Blues their 46th point of the season.
Blues: A Janata, S Robbins, A Mason, J Thomas (I Nkosi 90), R Henshaw, A Bailey-Dennis, J Renee, G Craddock (R Charles (58), A Warman, L Callander, B Worman. Unused subs: B Sampayo, J Cureton