Former star Theo Walcott did the damage for the visitors, though Pierre-Emerick Aubameyang was able to claim a crucial equaliser.
But who were the best and worst performers from both sides?
✔️ GOOD PERFORMANCE
Eddie Nketiah: 7.0
The young Gunners forward isn't given many starts in the league these days, being largely kept for Europa League, but here he started and was one of the few bright spots in what was a distinctly average Arsenal display.
He set himself up between the posts and made life difficult for the defenders, and he was rewarded by his canny touch laying the ball into the path of Pierre-Emerick Aubameyang for what proved to be a vital equaliser.
❌ BAD PERFORMANCE
Stuart Armstrong: 5.4
It wasn't an evening to remember for the Southampton midfielder, who racked up a pass completion of just 63% on his 30 passes.
He had two shots well off target as well as winning just one of his six duels and going 0/1 on tackles too, in a largely ineffective display.
Nicolas Pepe: 6.1
It was another opportunity for the former Lille wide man to show what he is capable of, and it was, largely, another failed experiment.
Very little of promise came from his side of the pitch. He managed just 35 touches and completed a single dribble before being replaced early in a largely ineffectual display.
⭐ STAR MAN
Theo Walcott: 7.6
There was no issue of the former Arsenal man celebrating scoring his excellent opening goal at the home of his former team.
Walcott sprinted clear of a static Arsenal back line to casually lift the ball over Bernd Leno and give his side the lead. The winger only played for 63 minutes but was by far Southampton's most agile attacking threat during his time on the pitch.