Arsenal kicked off the new year in style with a superb 2-0 win over Manchester United, handing Mikel Arteta his first victory in charge of the Gunners.
Arsenal - transformed from the blunt, directionless outfit of recent months into a high-intensity side by Arteta - struck at the beginning and end of the first half, with the impressive Nicolas Pepe (8) tucking in before Sokratis (42) smashed home a close-range finish to put the hosts in control.
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They were then pinned back for large periods after the break by a much-improved second-half display from Manchester United but, days after their collapse against Chelsea, stood firm to record their first clean sheet at the Emirates in three months.
The win moves Arsenal to within three points of the top six in 10th place in the Premier League, while United's recent surge towards the Champions League places stalls, with Ole Gunnar Solskjaer's men remaining five points off fourth.
The story of Arteta's first win…
Marcus Rashford had an effort at goal from distance inside a minute but it was Arsenal who struck early, just as they had against Chelsea on Sunday.
Arsenal: Leno (8), Maitland-Niles (8), Sokratis (9), David Luiz (8), Kolasinac (8), Torreira (8), Xhaka (7), Pepe (8), Ozil (8), Aubameyang (7), Lacazette (7).
Subs used: Nelson (6), Guendouzi (6), Saka (7).
Man Utd: De Gea (6), Wan-Bissaka (6), Maguire (6), Lindelof (6), Shaw (5), Fred (6), Matic (6), Rashford (6), Lingard (5), James (6), Martial (6).
Subs used: Pereira (7), Greenwood (6), Mata (n/a).
Man of the match: Sokratis (Arsenal)
Sead Kolasinac combined with Pierre-Emerick Aubameyang on the left flank and his deflected cut-back was slotted home by the unmarked Pepe for his fifth goal in an Arsenal shirt.
Mikel Arteta made four changes, with Nicolas Pepe making his first start under the new boss and Granit Xhaka, Sokratis and Sead Kolasinac returning.
There was no Paul Pogba in Manchester United's squad, with Aaron Wan-Bissaka, Luke Shaw and Jesse Lingard forming the three changes.
The Ivorian then teased Luke Shaw - as he continued to do throughout the match - before teeing up Aubameyang to fire over as Arsenal took control of the opening period.
Alexandre Lacazette miscued wide after a smart turn in the box just after the half-hour before Pepe smacked the upright with a low, left-foot curler from the edge of the area as Arsenal began to make their dominance tell.
The deserved second came just before the break when Lacazette flicked on a corner and United 'keeper David de Gea was only able to parry the ball into Jesse Lingard's back, allowing Sokratis to smash home the second.
United came out strongly after the break, though, and moments after Daniel James had warmed the hands of Bernd Leno with a low drive, his replacement Andreas Pereira slammed a shot into the side-netting.
Arsenal continued to carry a threat on the break, with Mesut Ozil, Aubameyang and Lacazette combining for a chance on 61 minutes, but United took control of possession and territory, with Rashford firing over after good work from Anthony Martial and then Aaron Wan-Bissaka seeing his penalty appeals rightly waved away after he went down under minimal contact from Aubameyang.
On the counter, Lacazette shot over, sub Bukayo Saka hit a tame one at De Gea and Aubameyang squandered another opportunity with a poor pass when presented with a chance to kill the game - but in the end a third was not required.
Arsenal, who had won just one of their previous 15 games, had crumbled in the final minutes to lose to Chelsea last time out but saw out the remaining minutes to land a significant win at the start of 2020.
What the managers said...
Mikel Arteta, Arsenal: "I am very pleased with the performance, I'm even more pleased with the result that we needed. A lot of the things I demanded and I wanted to see on the pitch actually happened today.
"At the moment we are suffering a little bit to maintain the level of intensity we are playing in the first half. I think it will come. It is part of the process and the way we train - but at the moment we don't have much time to do so."
Ole Gunnar Solskjaer, Man Utd: "After they scored the first goal it seemed like they had loads of energy. Their heads got loads of energy and ours were a little bit tired. They were the better team, aggressive, regained the ball we couldn't find a way out of their press. It was hard to get the ball off them because I thought they played really well.
"It was a good game by two good teams and the goal just before half time was a killer blow. At 1-0 you're in the game all the time, at 2-0 you need a goal to get that energy to make them nervous again. That was disappointing."
- Arsenal ended a run of seven home games without a win in all competitions to register their first win at the Emirates since a 3-2 win over Vitória Guimarães in the Europa League in October.
- Manchester United have now lost four of their last five away Premier League visits to Arsenal (W1).
- Arsenal are unbeaten in their last 11 home top-flight matches on New Year's Day (W9 D2), winning their last seven in a row.
- This was Arsenal's first Premier League win this season against a team currently in the top-half of the Premier League (P10 W1 D4 L5).
- Nicolas Pépé has scored all five of his goals for Arsenal in all competitions in London - four at the Emirates and one at London Stadium.
- Arsenal boss Mikel Arteta is the seventh manager to register his first Premier League victory in a game against Manchester United, and the first since Darren Moore in April 2018 with West Brom.
- Arsenal have scored eight goals via corners in the Premier League this season, two more than any other team.
Arsenal host Leeds in the FA Cup third round on Monday, while Manchester United travel to Wolves on Saturday for their own third-round FA Cup tie.