Arsenal 0, Southampton 2
Arsenal manager Arsene Wenger defended his decision to make 10 changes after the Gunners crashed out of the EFL Cup at home to Southampton for the second time in three seasons on Wednesday night.
First-half goals from Jordy Clasie and Ryan Bertrand ended Arsenal's 19-match unbeaten run in all competitions and sent the Saints into a first League Cup semi-final since 1987, where they will face Liverpool.
Wenger rested stars such as Alexis Sanchez, Mesut Ozil, Theo Walcott, Petr Cech, Laurent Koscielny and Shkodran Mustafi but said: "I don't think the problem was there. We had players used to top level competition but we didn't have the right urgency from the start.
"We had a disappointing performance especially in the first half and gave ourselves a mountain to climb. We weren't good enough in defence and gave cheap goals away.
"It was one of those nights where it looks like you can play two hours without scoring. We had not enough urgency in the first half and were weak in some departments - and we paid for that."
Wenger admitted he still does not know when Santi Cazorla will return from an inflamed Achilles but revealed Olivier Giroud could overcome a minor strain for Satirday's trip to West Ham and long-term absentee Danny Welbeck will return to full training this month.
For all of Arsenal's squad rotation, Claude Puel - who played under Wenger at Monaco - himself made eight changes to the Saints team that beat Everton on Sunday, yet they were comfortably superior throughout.
Clasie fired Southampton ahead in the 12th minute when Bertrand crossed for Sofiane Boufal, his shot was blocked by Rob Holding and the diminutive midfielder drove the loose ball emphatically past wrong-footed goalkeeper Emiliano Martinez.
The Saints doubled their lead with another raid down the left seven minutes before half-time.
Gunners full-back Carl Jenkinson was dispossessed, Boufal cut inside and rolled across the edge of the box for Bertrand, whose shot trickled low into the far corner.
Southampton's £16m record signing Boufal saw his shot deflected inches wide as the visitors remained the more potent side after the break, and Shane Long should have added a third instead of shooting wide when through on goal 12 minutes from time.