Declan Rice was positioned in the right place to push the Hammers into a lead early in the second half, converting into Bernd Leno's top-right corner after Felipe Anderson's creative run down the right flank.
Unai Emery's side struggled to challenge West Ham goalkeeper Lukasz Fabianski, and they failed to score in a match for the first time since their defeat to Manchester City on the opening day of the season.
Aubameyang Won't Emulate Dortmund Form in Emery's System
Arsenal signed a genuinely world-class finisher and one of the best forwards in Europe when they spent a club-record £56 million on Pierre-Emerick Aubameyang in January, but his impact has been diminished by the tactics deployed by Emery.
A record of 26 goals in 41 games for the club since then is impressive, but Gunners fans saw on Saturday—not for the first time this season—how restricted their star is under Emery's regime. After all, the north Londoners know what they could get from a striker who scored 141 times in 213 games for Borussia Dortmund.
Alexandre Lacazette is often the man trusted to roam forward as Arsenal's focal point, with Aubameyang regularly tucked just behind and Alex Iwobi also frequently functioning in a similar role this term.
Granted, the team are still adjusting to Emery's blueprint, but the fact is that when you have a forward as prolific as Aubayemang, you often want them positioned closest to the opposition defence.
Sportswriter Jame Benge showed after Saturday's first half how that was not the case at London Stadium:
Aubameyang almost looked like a midfielder at times, where one might expect to see Henrikh Mkhitaryan pop up as playmaker, and as such, his presence in the West Ham box was almost unnoticeable at times.
Arsenal were especially weak in attack during the first half, and even then it wasn't Aubameyang imposing himself on the Hammers back line, per Match of the Day:
Blogger Adam Keys also had a bone to pick with Aubameyang's general disposition and lack of aggression, which most of West Ham's side displayed in spades:
Altogether, Aubameyang had 29 touches against West Ham, per WhoScored.com—the only player who started and had fewer was West Ham striker Marko Arnautovic, who went off after 71 minutes.
Emery has had mixed fortune operating with a front forward pair since taking over at the Emirates in the summer, but their impetus should be on optimising Aubameyang and Lacazette, not one or the other.
Malleable though the Gabonese star may be, Aubameyang is at his best in front of goal but will struggle to find his way there with as much ease under Emery's guidance.
Samir Nasri Will Prove Well Worthy of West Ham's Risky Investment
The script was written for former Gunner Samir Nasri to have an impact against old club Arsenal after he was named in Manuel Pellegrini's XI, marking his return to the Premier League two-and-a-half years after his last appearance in the competition.
And it was Nasri who supplied the crucial last poke into the danger area before Rice powered home the breakthrough strike at London Stadium, via NBC's Joe Prince-Wright (U.S. only):
Perhaps it shouldn't come as any surprise for a player who was a contender for PFA Player of the Year during his Arsenal days, and the Evening Standard's Jack Rosser flattered the Frenchman upon his return:
After stints with Sevilla in Spain and Antalyaspor in Turkey, as well as an 18-month ban from football for doping, it's understandable there might be concerns as to whether Nasri can still cut it. A 71-minute cameo against one of the Premier League's elite suggested the Hammers have got their hands on a bargain.
Nasri is now 31 and hasn't enjoyed consistent play in the last few years, but Pellegrini worked with the playmaker for several years at the Etihad Stadium and clearly knows the player he's brought in on a free.
Sportswriter Daniel Storey joked about the player's lack of match fitness:
The Premier League is where Nasri has enjoyed the highlights of his career, winning two Premier League titles during his time with City and producing arguably the best football of his career in Arsenal colours.
Now he's back in England's capital and ready to sparkle as part of a smaller organisation in West Ham, though Saturday's performance showed he still boasts supreme quality and will be a major asset to his new side.
Arsenal will have no respite following their latest defeat as they're due to face Chelsea at the Emirates Stadium next Saturday, while West Ham will chase a second successive victory away to Bournemouth on the same day.