Brighton & Hove Albion ruined Chelsea boss Frank Lampard's return to Stamford Bridge with a 2-1 comeback win on Saturday as substitutes Danny Welbeck and Julio Enciso condemned the Blues to a third defeat in three games under their interim coach.
Lampard, who rested several first-choice starters before Tuesday's Champions League quarter-final second leg against Real Madrid, saw the Blues score the first goal of his second spell in charge when Conor Gallagher's heavily deflected shot beat Robert Sanchez in the Brighton goal in the 13th minute.
But the visitors, under coach Roberto De Zerbi, were the better side for long spells of the match and drew level when Welbeck squeezed between two defenders to head in off the post in the 42nd minute.
The Seagulls got the second goal that they deserved when Enciso scored with an unstoppable shot from 25 yards in the 69th minute, bolstering Brighton's hopes of European football for the first time in their history next season.
Brighton hammered Chelsea 4-1 in October, a result which set in train a slump in form for the London side that led to the dismissal this month of Graham Potter as coach, six months after the Blues had poached him from the south-coast side.
The result left Brighton seventh in the Premier League, five points ahead of Liverpool. Chelsea remain marooned in 11th position with their only hope of any silverware this season dependent on their ability to turn around a 2-0 deficit against reigning European champions Real Madrid at home on Tuesday.