The hosts flew out of the blocks and opened the scoring, albeit in fortuitous circumstances in the third minute.
Paul Hartley's corner was cleared to Bradley Orr 30-yards from goal and his low return drive hit City defender Liam Fontaine, who somehow diverted the ball beyond the hapless Lee Camp, who had no chance of making the save.
But it's 36 years and 18 games since City last beat Forest in the league and their lead vanished just short of the half-hour.
Guy Moussi hit a 30-yard thunderbolt to restore parity for the visitors and it was an effort appreciated by away and home fans alike as the sun appeared at a rain soaked Ashton Gate.
Forest rested their first-choice strikers and handed Dele Adebola a rare start against his old club but he lasted an hour, leaving with a muscle strain.
The second half was going nowhere until Tyson arrived in the 67th minute, replacing George Boyd and inside a minute, he forced a late save from Gerken.
The goalkeeper made an even more memorable stop from another sub, Joe Garner, before his injury brought about a sour ending.
Tyson's studs-up challenge brought a lengthy halt to proceedings as Gerken left on a stretcher and in obvious discomfort.
Striker Stefan Maierhofer, who is on loan from Wolves, took over in goal with City's three substitutions already on the field, but wasn't required to make a save as the game ended in a score-draw.