Derksen finished with 17 points and 12 rebounds and Watson added 15 points in the season opener for both teams.
Nate Renfro's layup gave San Francisco the lead for good at 75-73 with 1:27 left. The Dons forced a stop, but UIC's Hassan Thomas stole it from Watson, giving the Flames a chance to tie or go ahead in the final 27 seconds.
Dikembe Dixson pulled UIC back within two with a pair of free throws, and then Watson made 1 of 2 to cap the scoring with 4.5 seconds left.
Dixson led the Flames with 13.