Interim Blues boss Calum McFarlane delivered an FA Cup semi-final win over Leeds United in his first game in charge, but any semblance of a new manager bounce went up in smoke inside two minutes.
Dilane Bakwa stood up a cross for Taiwo Awoniyi, who rose to guide a lovely header past Robert Sanchez, seizing his opportunity amid Vitor Pereira’s wholesale changes.
Enzo Fernandez came close to a quick response, but his curling effort struck the far post, and things soon went from bad to worse for the hosts.
Another cross from the right seemed to panic Malo Gusto, who tugged back Awoniyi, leaving the VAR with no choice but to award a penalty. Igor Jesus converted it, with the home fans left shell-shocked by yet another new low.
Morato was the only survivor in defence from the Tricky Trees’ European endeavours, and the 24-year-old was the most experienced figure in the back line, which featured a full debut for Luca Netz and just a second league start for 19-year-old Zach Abbott.
It was a moment of inexperience from the full-back that gave Chelsea a little-merited chance to get back into the contest on the brink of half-time, going for the ball with debutant Jesse Derry, but prompting a nasty clash of heads in the process.
There was a 10-minute wait as the Blues youngster was stretchered from the field, and Cole Palmer could not keep his cool, with Matz Sels denying him smartly from the penalty spot.
Levi Colwill’s long-awaited return was a welcome start to the second half, but it was the Forest bench that made the more telling contribution, with Morgan Gibbs-White coming on to assist Awoniyi for his second of the match following a VAR check on a tight offside call.
The playmaker’s stint in the game was short-lived, however, as another nasty collision forced both him and Chelsea goalkeeper Sanchez from the field.
Joao Pedro thought he had at least ended his side’s nine-hour wait for a Premier League goal, but his would-be consolation was chalked off for offside.
He did belatedly put an end to the dire drought in stoppage time, doing so in style with a picture-book bicycle kick, but the contest was long since settled.
Chelsea have now lost six league games in a row, and their worst run since an equivalent sequence of defeats in 1993 leaves them in ninth place, with the top five now mathematically out of reach.
Forest move six points clear of the drop zone with three games left, having effectively secured safety courtesy of a seven-game undefeated run, and their attention will now turn to their UEFA Europa League semi-final second-leg matchup with Aston Villa.