Brighton have won their past three matches at Emirates Stadium in the league and cupArsenal's fading title hopes were dealt a devastating blow after losing to Brighton to leave leaders Manchester City one win from a fifth Premier League title in six seasons.
The Gunners needed to respond after City's 3-0 win over Everton earlier on Sunday left Mikel Arteta's side trailing by four points in the race for the title.
On a deeply frustrating day for Arsenal, Leandro Trossard hit the bar against his former club while Martin Odegaard and Bukayo Saka both went close before Julio Enciso's close-range header put Brighton ahead.
Substitute Deniz Undav doubled the lead after lobbing Aaron Ramsdale in the 86th minute before Pervis Estupinan added to Arsenal's misery with Brighton's third in the 96th minute.
City will win the Premier League title next Sunday in front of their own fans if they beat Chelsea at home (16:00 BST), even if Arsenal defeat Nottingham Forest at the City Ground on Saturday (17:30).
However, City will be confirmed champions without playing on Saturday if the Gunners lose at Forest.
In a game littered with niggly fouls, Arsenal lost Brazil forward Gabriel Martinelli to injury in the first half after a foul by Brighton's Ecuador midfielder Moises Caicedo, who the Gunners tried to sign in January.
Brighton, who are chasing a place in Europe for the first time, had gone close through Enciso before the Paraguay forward stunned the Emirates with his 51st-minute goal.
The win lifted the Seagulls above both Aston Villa and Tottenham into sixth on 58 points, four behind fifth-placed Liverpool with one game in hand.
The maximum number of points Arsenal can score is 87, while City have 85 with matches against Chelsea (home), Brighton (away) and Brentford (away) to come.
Arsenal's title challenge runs out of steam
Arsenal's players sank to their knees after the full-time whistle, the realisation quickly sinking in that their title dream was all but over after being picked apart by Brighton.
The Gunners deserve enormous credit for the way they have pushed Manchester City in the title race. They were eight points clear of City at the top after 18 games but their pursuit is running out of steam after a highly damaging defeat at the business end of the season.
Manchester City's comfortable win at Everton earlier on Sunday opened up a four-point gap at the top but this time Arsenal were unable to respond to the pressure heaped on them by Pep Guardiola's Treble-chasing team.
There was still almost 40 minutes left when Enciso opened the scoring and Arteta sent on Eddie Nketiah and Emile Smith Rowe to try and salvage a point.
But the Arsenal boss, who was shown a yellow card by referee Andy Madley, saw his side concede two further goals as the home side failed to find the net for the first time since 4 February on their way to a comprehensive defeat.
Brighton's incredible season far from over
This was another statement win in what looks like being a history-defining season for Brighton, who bounced back from a crushing 5-1 home defeat by Everton to produce one of their best performances of the season.
They were at their clinical best as Arsenal were beaten at the Emirates for only the second time in the league.
Roberto De Zerbi has called on his players to "write club history" by qualifying for Europe for the first time.
Two wins from the last four games - Newcastle (away), Southampton (home), Manchester City (home), Aston Villa (away) - will be enough to see the Seagulls confirm their place in next season's Europa League.
Against Arsenal, Brighton were at their attacking best, registering six chances on target and scoring from half of them.
As Arsenal's players looked desolate at the final whistle, Brighton's triumphantly marched over to where their travelling fans were gathered to show their appreciation.
This incredible season for the Seagulls, which has included an FA Cup semi-final and league doubles over Manchester United and Chelsea, is far from over.
Player of the match
DunkLewis Dunk
Line-ups
Arsenal
Formation 4-3-3
1Ramsdale
4White15Kiwior6Gabriel3Tierney
8Ødegaard20Jorginho34Xhaka
7Saka9Gabriel Jesus11Martinelli
1Ramsdale4White15Kiwior6Gabriel3Tierney8ØdegaardSubstituted forSmith Roweat 77'minutes20JorginhoSubstituted forParteyat 60'minutesBooked at 88mins34XhakaSubstituted forNelsonat 60'minutes7Saka9Gabriel JesusSubstituted forNketiahat 77'minutes11MartinelliSubstituted forTrossardat 20'minutesSubstitutes
5Partey10Smith Rowe14Nketiah16Holding19Trossard21Fábio Vieira24Nelson30Turner97WaltersBrighton
Formation 4-2-3-1
23Steele
25Caicedo5Dunk6Colwill30Estupiñán
13Groß27Gilmour
22Mitoma10Mac Allister20Enciso
28Ferguson
23Steele25Caicedo5Dunk6Colwill30EstupiñánBooked at 34mins13GroßBooked at 55mins27GilmourSubstituted forWelbeckat 60'minutes22Mitoma10Mac Allister20EncisoSubstituted forUndavat 82'minutes28FergusonSubstituted forBuonanotteat 77'minutesSubstitutes
18Welbeck21Undav26Ayari29van Hecke38McGill40Buonanotte42Offiah49Moran51PeupionReferee:Andy MadleyAttendance:60,139Live Text
Match ends, Arsenal 0, Brighton and Hove Albion 3.
Second Half ends, Arsenal 0, Brighton and Hove Albion 3.
Goal! Arsenal 0, Brighton and Hove Albion 3. Pervis Estupiñán (Brighton and Hove Albion) left footed shot from the centre of the box to the high centre of the goal.
Attempt saved. Deniz Undav (Brighton and Hove Albion) right footed shot from outside the box is saved in the bottom left corner. Assisted by Danny Welbeck.
Attempt blocked. Reiss Nelson (Arsenal) right footed shot from the left side of the box is blocked. Assisted by Thomas Partey.
Offside, Brighton and Hove Albion. Levi Colwill tries a through ball, but Pervis Estupiñán is caught offside.
Moisés Caicedo (Brighton and Hove Albion) wins a free kick in the defensive half.
Foul by Reiss Nelson (Arsenal).
Attempt blocked. Kaoru Mitoma (Brighton and Hove Albion) right footed shot from the centre of the box is blocked. Assisted by Deniz Undav.
Hand ball by Deniz Undav (Brighton and Hove Albion).
Thomas Partey (Arsenal) is shown the yellow card for a bad foul.
Kaoru Mitoma (Brighton and Hove Albion) wins a free kick in the defensive half.
Foul by Thomas Partey (Arsenal).
Goal! Arsenal 0, Brighton and Hove Albion 2. Deniz Undav (Brighton and Hove Albion) left footed shot from the centre of the box to the centre of the goal. Assisted by Pascal Groß.
Foul by Deniz Undav (Brighton and Hove Albion).
Thomas Partey (Arsenal) wins a free kick in the defensive half.
Attempt saved. Deniz Undav (Brighton and Hove Albion) right footed shot from outside the box is saved in the centre of the goal.
Attempt missed. Gabriel Magalhães (Arsenal) right footed shot from the centre of the box is close, but misses to the right. Assisted by Thomas Partey following a corner.
Corner, Arsenal. Conceded by Lewis Dunk.
Attempt blocked. Reiss Nelson (Arsenal) left footed shot from a difficult angle on the left is blocked. Assisted by Eddie Nketiah.
Our coverage of your Premier League club is bigger and better than ever before - here's everything you need to know to make sure you never miss a moment
