MANCHESTER, England -- Paul Pogba walked off the pitch alone after once again playing a central role in Manchester United's downfall. The France international midfielder's needless foul on Hector Bellerin on 68 minutes resulted in the penalty from which Pierre-Emerick Aubameyang scored to seal Arsenal's first league victory at Old Trafford since 2006.

Pogba, who has always lacked defensive qualities, conceded another penalty in the 6-1 home defeat against Tottenham last month when a similarly thoughtless challenge on Ben Davies led to a penalty for the opposition.

This is the problem with Pogba. Ole Gunnar Solskjaer can only rely on the £89 million player to let him down, so it raises the question as to why the United manager continues to trust him with a place in the team. United's defeat against Arsenal is not a Pogba story, but he does embody the reason Solskjaer is still going around in circles after 100 games in charge and why Gunners boss Mikel Arteta is instead driving his team forward in more convincing fashion.

- Stream ESPN FC Daily on ESPN+ (U.S. only)
- Predict results in ESPN's English Soccer Pick 'Em!
- ESPN+ viewer's guide: Bundesliga, Serie A, MLS, FA Cup and more

When Arteta took charge at the Emirates last December, he inherited a talented, but unreliable, midfielder in Mesut Ozil. Less than a year into the job, Arteta has cast Ozil into the wilderness and built a plan without the German. That decision emphasises the certainty and conviction of the Spaniard and it is now showing through in his team.

As for Solskjaer, nobody quite knows where United are heading, and Pogba sums up how the team are drifting towards the doldrums.

Yes, they have beaten Paris Saint-Germain and RB Leipzig in the Champions League this season, but United now lie 15th in the Premier League, with seven points from six games, and have failed to win any of their first four home league games for the first time since the 1972-73 season. The Solskjaer cheerleaders can celebrate the Champions League wins all they like, but the club's bread and butter is the Premier League. United are already nine points behind leaders Liverpool, so forget about the title for another year.

Not so long ago, United versus Arsenal was the game that mattered in the Premier League. Between 1996 and 2004, the two teams won nine titles between them in nine seasons. Those days are long gone -- Arsenal haven't won the title since 2004, United since 2013 -- but they are such big clubs that they should both be much closer to the top than they are right now.

But despite having been at Arsenal for less than half the time that Solskjaer has been at United, Arteta clearly has his team on the route to recovery by imposing a coherent plan, which includes signing players to solve clear problems. This was the first time since a victory at Manchester City in January 2015 -- a run of 29 games -- that Arsenal have won away at a so-called Big Six opponent, and the win had Arteta's fingerprints all over it.

Two of his big summer signings -- defender Gabriel and midfielder Thomas Partey -- were crucial figures in this win. Gabriel, with his aggression and organisation skills, ensured a solid back line for Arsenal and he also kept Marcus Rashford and Mason Greenwood quiet. And Partey dominated the midfield, albeit against a United side that struggled to make its diamond formation work.

Until Arteta arrived to replace the sacked Unai Emery 11 months ago, Arsenal's problems at the back and in midfield had become an embarrassment, problems that Emery and Wenger had somehow failed to address. But Arteta has dealt with both already and his strategic summer recruitment has been key to that.

In contrast, Solskjaer and United have once again paid the price for a shambolic summer window. Netherlands midfielder Donny van de Beek, the £40m buy from Ajax, has yet to start a league game, but with Pogba and Bruno Fernandes already playing in his favoured position, why sign him in the first place? United needed a commanding centre-half and defensive midfielder, just like Arsenal did, but they failed to address either issue.

Arteta got what he wanted and needed, but Solskjaer ended up with a midfielder he hadn't targeted and two gaping holes left unfilled.

But it isn't all about signings either. Tactically, Solskjaer was taken back to school by Arteta, who used wing-backs Bellerin and Kieran Tierney out wide to take advantage of the lack of width caused by United's diamond formation. The pair caused havoc all afternoon -- the contrast of United full-backs Luke Shaw and Aaron Wan-Bissaka was striking -- and Solskjaer sat on his hands as United were crying out for a change of approach.

But Solskjaer has never shown much certainty or direction as United manager, so it is little surprise that his team plays in the same fashion. Arteta, meanwhile, has Arsenal playing in his image in a positive manner, and his team is looking good.

These two clubs will eventually get it right again, but the smart money would be on Arsenal getting there first.