Chelsea boss Thomas Tuchel says his side need to "toughen up and show a different mentality" after they were beaten by Southampton at St Mary's.
The German boss criticised "soft, soft, soft defending" in what was the Blues' second defeat in their opening five Premier League games this season.
Raheem Sterling put the visitors ahead but Romeo Lavia and Adam Armstrong responded as Southampton won 2-1.
"It is not enough to play 20-25 minutes on the level we want," said Tuchel.
Chelsea's other defeat also came away from home in a 3-0 humbling by Leeds at Elland Road last week.