Chris Coleman’s side have crashed into League One only a year after being relegated from the Premier League.
They have played only one season outside the top two tiers of English football in their entire history, winning promotion from the old Third Division in 1987-88.
Burton striker Darren Bent returned to haunt his former team with an 86th-minute equaliser to cancel out Paddy McNair’s opener on 34 minutes at the Stadium of Light.
Liam Boyce headed second-bottom Burton in front in second half stoppage-time before Sunderland had a late equaliser disallowed to provide a fitting finale to their wretched season.
Sunderland are six points from safety with only two matches left and the remaining fixtures of their relegation rivals make it mathematically impossible to avoid the drop.