Pierre-Emerick Aubameyang is the first player since Alexis Sanchez to reach 20 goals in a single campaign for Arsenal
Ole Gunnar Solskjaer suffered his first Premier League defeat since being appointed Manchester United's interim manager as Arsenal leapfrogged their opponents to move into the top four.
Switzerland midfielder Granit Xhaka beat David de Gea with a swerving shot from outside the penalty area, which the United keeper was expected to stop.
Romelu Lukaku hit the bar while the game was goalless, when it appeared easier to score, and Brazilian midfielder Fred struck a post for United.
Arsenal keeper Bernd Leno also produced two crucial saves to keep out Lukaku, before Pierre-Emerick Aubameyang doubled the hosts' lead from the penalty spot after Fred's foul on Alexandre Lacazette.
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Man Utd's Smalling shoved by fan
Reaction from Emirates Stadium
Soon after Arsenal's second goal, a fan ran on to the pitch and shoved United defender Chris Smalling before being removed by stewards.
The Gunners have won seven out of 10 top-flight games in 2019 and are one point behind north London rivals Tottenham, who sit third in the table, with eight games remaining.
United, who started the weekend in fourth, drop to fifth in the race for a Champions League spot next season.
Arsenal turn on the style to sink United
Last weekend, Aubameyang left Wembley dejected after his last-minute penalty was saved by Tottenham keeper Hugo Lloris to deny Arsenal victory in the North London derby.
Against United, he stepped forward and beat De Gea from the spot to seal a first win over United in six league and cup meetings.
It was awarded after Fred's forearm nudged into Lacazette, sending the French forward tumbling inside the box.
Lacazette inspired one of Arsenal's finest days under Unai Emery's command.
The Gunners were sharp, lively and industrious as they made amends after United eliminated them from the FA Cup six weeks ago.
Emery named six players who started Thursday's Europa League defeat by Rennes in his starting line-up, but there was little sign of fatigue as the hosts came flying out of traps.
They opened the scoring with their only shot on target in the first half, Xhaka deceiving De Gea with a shot that left the United keeper rooted to his line.
Leno was also key for Gunners.
The German did well to frustrate Lukaku as the Belgium forward threatened to go around and equalise, before denying the same player with an outstretched leg after half-time.
Arsenal have now played all their Champions League chasing rivals - a place in Europe's most prestigious competition next season is very much in their own hands.
More to follow.
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Line-ups
Match Stats
Live Text
Line-ups
Arsenal
19Leno
5PapastathopoulosBooked at 38mins
6Koscielny
18Monreal
15Maitland-Niles
8Ramsey
34Xhaka
31KolasinacBooked at 90mins
10ÖzilSubstituted forIwobiat 77'minutes
9LacazetteSubstituted forNketiahat 86'minutes
14AubameyangSubstituted forD Suárezat 80'minutes
Substitutes
1Cech
4Elneny
17Iwobi
20Mustafi
22D Suárez
29Guendouzi
49Nketiah
Man Utd
1De Gea
18Young
12Smalling
2Lindelöf
23Shaw
20DalotSubstituted forMartialat 71'minutes
17Fred
31MaticBooked at 68minsSubstituted forGreenwoodat 80'minutes
6PogbaBooked at 76mins
10Rashford
9Lukaku
Substitutes
3Bailly
11Martial
15Pereira
16Rojo
22Romero
39McTominay
54Greenwood
Referee:
Jonathan Moss
Attendance:
60,000
Match Stats
Home TeamArsenalAway TeamMan Utd
Possession
Home46%
Away54%
Shots
Home14
Away14
Shots on Target
Home3
Away4
Corners
Home5
Away2
Fouls
Home12
Away18
Live Text
Posted at
Match ends, Arsenal 2, Manchester United 0.
Full TimePosted at 90'+6'
Second Half ends, Arsenal 2, Manchester United 0.
Posted at 90'+2'
Attempt saved. Marcus Rashford (Manchester United) header from the centre of the box is saved in the centre of the goal. Assisted by Ashley Young with a cross.
BookingPosted at 90'
Sead Kolasinac (Arsenal) is shown the yellow card for a bad foul.
Posted at 89'
Mason Greenwood (Manchester United) wins a free kick in the defensive half.
Posted at 89'
Foul by Sead Kolasinac (Arsenal).
Posted at 89'
Foul by Luke Shaw (Manchester United).
Posted at 89'
Eddie Nketiah (Arsenal) wins a free kick on the right wing.
SubstitutionPosted at 86'
Substitution, Arsenal. Eddie Nketiah replaces Alexandre Lacazette.
Posted at 86'
Foul by Luke Shaw (Manchester United).
Posted at 86'
Denis Suárez (Arsenal) wins a free kick in the defensive half.
Posted at 84'
Foul by Ashley Young (Manchester United).
Posted at 84'
Alex Iwobi (Arsenal) wins a free kick on the left wing.
SubstitutionPosted at 80'
Substitution, Arsenal. Denis Suárez replaces Pierre-Emerick Aubameyang.
SubstitutionPosted at 80'
Substitution, Manchester United. Mason Greenwood replaces Nemanja Matic.
Posted at 80'
Foul by Fred (Manchester United).
Posted at 80'
Sead Kolasinac (Arsenal) wins a free kick on the left wing.
Posted at 79'
Offside, Manchester United. Luke Shaw tries a through ball, but Chris Smalling is caught offside.
Posted at 78'
Luke Shaw (Manchester United) wins a free kick in the attacking half.
Posted at 78'
Foul by Pierre-Emerick Aubameyang (Arsenal).
Posted at 77'
Sokratis (Arsenal) wins a free kick in the defensive half.
Posted at 77'
Foul by Romelu Lukaku (Manchester United).
SubstitutionPosted at 77'
Substitution, Arsenal. Alex Iwobi replaces Mesut Özil.
BookingPosted at 76'
Paul Pogba (Manchester United) is shown the yellow card for a bad foul.
Posted at 76'
Granit Xhaka (Arsenal) wins a free kick in the attacking half.
Posted at 76'
Foul by Paul Pogba (Manchester United).
Posted at 74'
Foul by Aaron Ramsey (Arsenal).
Posted at 74'
Paul Pogba (Manchester United) wins a free kick in the defensive half.
Posted at 74'
Foul by Granit Xhaka (Arsenal).
Posted at 74'
Fred (Manchester United) wins a free kick in the defensive half.
Posted at 74'
Attempt blocked. Sokratis (Arsenal) header from the centre of the box is blocked. Assisted by Granit Xhaka with a cross.
Posted at 74'
Corner, Arsenal. Conceded by Ashley Young.
Posted at 73'
Aaron Ramsey (Arsenal) wins a free kick in the defensive half.
Posted at 73'
Foul by Paul Pogba (Manchester United).
Posted at 72'
Offside, Arsenal. Sokratis tries a through ball, but Pierre-Emerick Aubameyang is caught offside.
Posted at 72'
Alexandre Lacazette (Arsenal) wins a free kick in the defensive half.
Posted at 72'
Foul by Luke Shaw (Manchester United).
Posted at 71'
Attempt missed. Alexandre Lacazette (Arsenal) right footed shot from the centre of the box is close, but misses to the left. Assisted by Sokratis with a headed pass.
SubstitutionPosted at 71'
Substitution, Manchester United. Anthony Martial replaces Diogo Dalot.
Goal!Posted at 69'
Goal! Arsenal 2, Manchester United 0. Pierre-Emerick Aubameyang (Arsenal) converts the penalty with a right footed shot to the centre of the goal.
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Source: bbc.com