The Guernsey teenager had already gone agonisingly close to scoring in the Championship encounter before he broke the deadlock on 39min. at Ashton Gate, knocking in the rebound after Nahki Wells had seen his shot saved by Brice Samba.
In the second half, Scott had a big appeal for a penalty dismissed before he was substituted with 13 minutes remaining and the home side still leading thanks to his goal.
However, Forest substitute Lyle Taylor made a major impact from the bench, initially converting a penalty just as four minutes of added time were announced.
The points looked to be shared but there was still time for the visitors to throw themselves forward again, and Taylor found himself in the right place at the right time as he put the ball over the line at the far post to inflict a cruel 2-1 defeat on the Robins.
'It’s a difficult one to take – we have thrown away a good situation tonight. It’s tough for our fans to come here week in week out and try and lift us with their support and for us not to be able to get over the line,' City manager Nigel Pearson told Robins TV afterwards.