Arsenal were stung by a late goal from Southampton's Shea Charles as the Premier League leaders fell to defeat in the FA Cup quarter-finals.
The match was Arsenal's first after their Carabao Cup final loss to Manchester City and followed an international break which was notable for 11 Gunners players withdrawing from their national teams because of injury.
However, Mikel Arteta was still able to name a side containing captain Martin Odegaard, Kai Havertz, Ben White and Gabriel Magalhaes, with Arsenal eager to clear this hurdle.
Despite Arsenal having such senior players in their ranks, and dominating possession, it was Southampton who were the side to create the better chances.
They were duly rewarded, with exuberant celebrations breaking out at full-time at St Mary's.
Now a Wembley trip awaits Southampton in the semi-finals, with Arsenal's hopes of a league and cup double crushed.
Championship promotion hopefuls Saints were on a 14-match unbeaten run coming into this game and their plan to get the ball forward quickly and behind the Arsenal defence caused the Gunners problems throughout.
It was from a floated ball into the penalty area that the home side took the lead in the 35th minute.
England defender White misjudged the flight of James Bree's delivery from the right, and that allowed Ross Stewart to control and swiftly plant a sweet finish past Kepa Arrizabalaga and into the right corner.
Arsenal manager Arteta made a triple change in the second half, with Viktor Gyokeres, Noni Madueke and Riccardo Calafiori coming on, but Southampton continued to threaten.
Tom Fellows flashed a ball just over the top of the Arsenal goal before the dangerous Leo Scienza hit the crossbar with a curling effort.
The visitors drew level when Gabriel's clever pass put Havertz through into the area and he cut the ball back for Gyokeres to level in the 68th minute.
But Southampton were not to be denied, and substitute Charles sent the home fans wild as he took on a short pass from Fellows and finished smartly into the bottom left corner.
Arsenal searched for a second equaliser but found it was beyond them, as Southampton reached the semi-finals for the first time since 2021.
