The Gunners, who meet Borussia Dortmund in the Champions League on Tuesday, are two points clear of Chelsea and Liverpool after the Reds had to settle for a point in a 2-2 draw against 10-man Newcastle.
Manchester City is three points off the pace after Sergio Aguero scored twice in a 3-1 win at West Ham for his club's first away victory this season.
Adam Lallana grabbed a late equalizer for Southampton in a 1-1 draw at United, adding to the defending champions' troubles in a lackluster start to their title defense.
Also, Everton beat Hull 2-1, Stoke was held to 0-0 by West Bromwich Albion, and Swansea defeated last-place Sunderland 4-0.
At St James' Park, Daniel Sturridge's header salvaged a point for Liverpool against 10-man Newcastle, but the England striker also missed a great opportunity to give the Reds the win in the closing stages when he completely misjudged his volley after being brilliantly picked out in the area by Steven Gerrard.
Yohan Cabaye's long-range strike put the Magpies ahead before Gerrard scored his 100th league goal for Liverpool, equalizing from the spot after defender Mapou Yanga-Mbiwa was sent off for a foul on Luis Suarez in the 40th.
Substitute Paul Dummet restored the home side's lead in the 57th with a shot at the far post against the run of the play but Sturridge headed home Suarez's precise cross in the 72nd.
``It's a chance missed for us today,'' Gerrard said. ``I thought we did enough to win it but credit to Newcastle for hanging in there. After the sending off the game changed. They started strongly but we dominated the rest of game but couldn't get enough goals to win it.''
Ahead of its Champions League trip to Schalke, Chelsea extended its unbeaten league run at home to 13 matches after recovering from a goal down against Cardiff and equalizing with a controversial goal which should have been disallowed.
Jordon Mutch put Cardiff in front before Eden Hazard leveled in the 33rd, set up by Eto'o who caught out Cardiff goalkeeper David Marshall while he was bouncing the ball, leading to Hazard scoring from close range. FIFA rules state the goalkeeper is still in possession at that point.
Eto'o made it 2-1 in the 66th before Oscar put the match to bed and Hazard scored his second of the afternoon.
Chelsea manager Jose Mourinho was sent to the stands before the third and fourth goals for berating the officials as Chelsea fans chanted ``Jose Mourinho, he sits where he wants.'' Mourinho climbed over the dugout and opted to sit next to a fan who tweeted: ``OMG morinho is sitting next to me.''
At Old Trafford, United took the lead in the 26th when Robin Van Persie scored from the rebound after Wayne Rooney's shot was saved by Artur Boruc.
Rooney then hit the crossbar with a volley moments later and Van Persie headed against the bar in the second half before Southampton leveled in the 89th as Lallana bundled in a corner from James Ward-Prowse.
``They had been knocking on the door but I thought we would see it out,'' United manager David Moyes said. ``But if you don't defend a corner well enough, there's always a chance they will score.''
United is eighth in the standings, eight points behind Arsenal.
City moved back into the top four after an excellent display from Aguero, who not only scored twice but also set up another goal. City opened up the Hammers' defense in the 16th minute when Aguero coolly broke the deadlock after Alvaro Negredo cleverly let Fernandinho's pass run through.
The Argentine doubled City's lead with a header, and West Ham pulled one back through Ricardo Vaz Te's acrobatic strike.
David Silva sealed City's win 10 minutes from time after Aguero turned provider.
-AP
