Teenager Julio Enciso scored a stunning winner as Brighton came from behind to beat Chelsea in the Premier League in Frank Lampard's first home match since being reappointed Blues manager.
Paraguayan forward Enciso, 19, blasted into the top corner from 35 yards to help Brighton continue their European qualification push.
Substitute Danny Welbeck had levelled at Stamford Bridge after Conor Gallagher's deflected strike gave Chelsea a fortunate lead.
Brighton remain seventh in the table and Chelsea 11th.
Enciso is Brighton's next big thing
Enciso became the latest Brighton youngster to hit the headlines as their shrewd deals in the transfer window continue to aid their drive up the table.
He joined for a reported £9.5m from Paraguayan club Libertad Asuncion in the summer and has slowly been bedded into the side.
He earlier hit a post from a tight angle just after the restart with Welbeck unable to prod home the rebound.
Brighton's controversial loss to Tottenham last Saturday ended their seven-match unbeaten run, but they dominated in west London even after conceding the opener.
Teenager Evan Ferguson struck the crossbar in the eighth minute, while Kaoru Mitoma forced a brilliant low save from Chelsea keeper Kepa Arrizabalaga midway through the first half.
Worryingly for Brighton, the in-form Ferguson landed awkwardly on an ankle after his header was tipped over the bar by Kepa.
He was replaced by Welbeck in the 39th minute and three minutes later the former Manchester United and Arsenal striker deservedly headed Pascal Gross' deep cross in off the post.
Victory lifted Brighton to within a point of sixth-placed Aston Villa, having played two games fewer.
They face United in the FA Cup semi-finals at Wembley on 23 April.
Chelsea end goal drought but still fall to defeat
Chelsea's opener ended a run of four games without a goal.
It was a fortunate strike too as Gallagher's shot deflected wickedly off defender Lewis Dunk and wrong-footed Brighton keeper Robert Sanchez, back in the team as a replacement for the injured Jason Steele.
Chelsea made six changes from their Champions League first-leg quarter-final loss to Real Madrid on Wednesday and looked disjointed throughout.
Their best chance came at the end of the first half, a Christian Pulisic header from close range striking the outside of the post.
Sanchez did well to keep out Reece James' cross and then Mykhailo Mudryk's follow-up early in the second half with the scores level.
Chelsea, who had never lost a home match to Brighton, find themselves 17 points off the top four, closer to the relegation zone than the Champions League spots.
They face Real in the second leg on Tuesday.
Player of the match
DunkLewis Dunk
Chelsea
Squad number23Player nameGallagher
Squad number1Player nameArrizabalaga
Squad number17Player nameSterling
Squad number21Player nameChilwell
Squad number5Player nameFernández
Squad number33Player nameFofana
Squad number4Player nameBadiashile
Squad number14Player nameChalobah
Squad number20Player nameZakaria
Squad number10Player namePulisic
Squad number24Player nameJames
Squad number11Player nameJoão Félix
Squad number15Player nameMudryk
Squad number19Player nameMount
Squad number8Player nameKovacic
Squad number22Player nameZiyech
Brighton & Hove Albion
Squad number5Player nameDunk
Squad number22Player nameMitoma
Squad number18Player nameWelbeck
Squad number20Player nameEnciso
Squad number10Player nameMac Allister
Squad number25Player nameCaicedo
Squad number7Player nameMarch
Squad number28Player nameFerguson
Squad number29Player namevan Hecke
Squad number13Player nameGroß
Squad number30Player nameEstupiñán
Squad number4Player nameWebster
Squad number1Player nameSánchez
Squad number34Player nameVeltman
Line-ups
Chelsea
Formation 4-2-3-1
1Arrizabalaga
14Chalobah33Fofana4Badiashile21Chilwell
20Zakaria5Fernández
10Pulisic23Gallagher15Mudryk
17Sterling
1Arrizabalaga14ChalobahBooked at 51mins33FofanaSubstituted forJamesat 57'minutes4Badiashile21Chilwell20ZakariaSubstituted forMountat 74'minutes5FernándezSubstituted forKovacicat 57'minutes10PulisicSubstituted forZiyechat 56'minutes23GallagherBooked at 45mins15Mudryk17SterlingSubstituted forJoão Félixat 57'minutesSubstitutes
8Kovacic9Aubameyang11João Félix16Mendy19Mount22Ziyech24James28Azpilicueta32CucurellaBrighton
Formation 4-2-3-1
1Sánchez
34Veltman4Webster5Dunk30Estupiñán
13Groß25Caicedo
7March10Mac Allister22Mitoma
28Ferguson
1SánchezBooked at 77mins34VeltmanBooked at 4minsSubstituted forEncisoat 28'minutes4WebsterSubstituted forvan Heckeat 86'minutes5Dunk30Estupiñán13Groß25Caicedo7March10Mac Allister22Mitoma28FergusonSubstituted forWelbeckat 39'minutesSubstitutes
18Welbeck20Enciso21Undav27Gilmour29van Hecke38McGill40Buonanotte42Offiah49MoranReferee:Robert JonesAttendance:40,126Live Text
Match ends, Chelsea 1, Brighton and Hove Albion 2.
Second Half ends, Chelsea 1, Brighton and Hove Albion 2.
Foul by Danny Welbeck (Brighton and Hove Albion).
Ben Chilwell (Chelsea) wins a free kick in the defensive half.
Attempt saved. Pascal Groß (Brighton and Hove Albion) left footed shot from the right side of the box is saved in the bottom right corner.
Attempt blocked. Danny Welbeck (Brighton and Hove Albion) left footed shot from the right side of the box is blocked.
Corner, Brighton and Hove Albion. Conceded by Ben Chilwell.
Attempt missed. Mykhailo Mudryk (Chelsea) right footed shot from outside the box is just a bit too high. Assisted by Ben Chilwell.
Corner, Chelsea. Conceded by Moisés Caicedo.
Foul by Pascal Groß (Brighton and Hove Albion).
Conor Gallagher (Chelsea) wins a free kick on the left wing.
Delay over. They are ready to continue.
Substitution, Brighton and Hove Albion. Jan Paul van Hecke replaces Adam Webster because of an injury.
Delay in match because of an injury Adam Webster (Brighton and Hove Albion).
Lewis Dunk (Brighton and Hove Albion) wins a free kick in the defensive half.
Foul by Hakim Ziyech (Chelsea).
Attempt missed. Mason Mount (Chelsea) right footed shot from outside the box is high and wide to the right.
Foul by Solly March (Brighton and Hove Albion).
Mason Mount (Chelsea) wins a free kick in the defensive half.
Robert Sánchez (Brighton and Hove Albion) is shown the yellow card.
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