Tam McManus and Eddie McCallion came on as Derry substitutes before Stoyanov scored the only goal.
BBC: CSKA Sofia 1-0 Derry City
2.
Longford almost went further in front, but Eddie McCallion cleared off the line.
BBC: Derry crash to Longford
3.
Substitute Tommy McCallion's superb through-ball split the Swifts defence and Patterson slotted past Rouse at his near post for his seventh league goal of the season.