Armstrong finished off a flowing team move involving Adam Armstrong and Mohamed Elyounoussi to stretch Saints’ unbeaten league run to three matches.
Granit Xhaka had given the Gunners an early lead with his second goal in as many games, sweeping the ball first time into the roof of the net from Ben White’s low delivery.
The effervescent Gabriel Martinelli had a shot deflected wide and Gabriel Jesus was denied by Southampton goalkeeper Gavin Bazunu as the visitors threatened to double their advantage before the interval.
Ralph Hasenhuttl’s team improved in the second half but needed a superb last-ditch challenge from Elyounoussi to deny Jesus, who had broken clear of the Southampton defense.
The result leaves Mikel Arteta’s team two points clear of second-placed Manchester City, while Saints stay in 15th – three points clear of the relegation zone.
Leave feedback about this