Thomas Tuchel said his Chelsea team were bullied by Southampton on Tuesday and urged them to toughen up for future Premier League away games.
The Blues lost 2-1 at St Mary's despite Raheem Sterling opening the scoring midway through the first half, as Romeo Lavia and Adam Armstrong struck to give the Saints their first home win over Chelsea since March 2013.
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Tuchel's side lost their second consecutive game on the road, having been roundly beaten 3-0 by Leeds United on Aug. 21, and now sit eighth in the table.
The disjointed display was a far cry from their 2-2 draw with Tottenham Hotspur on Aug. 14, when the Blues were unlucky not beat Spurs in a high-octane game which saw both managers sent off after the final whistle.
Since then, Chelsea have lost N'Golo Kante to a hamstring injury and picked up red cards in successive matches as Kalidou Koulibaly was sent off at Leeds before Conor Gallagher was dismissed in Saturday's 2-1 win over Leicester City.
Reece James was also absent against Southampton due to illness. Tuchel likened the current situation to the aftermath of a 4-0 victory over Juventus in November 2021 as they won just four of their next nine games and lost players to injury.
"You know what it reminded me of? About Juventus last season," Tuchel said after the match. "We played a fantastic match against Juventus at Stamford Bridge last season and after that we had 'Chilly' [Ben Chilwell] off for eight months and N'Golo Kante for three months and it was the same against Tottenham.
"We had a fantastic performance. After that our key player says goodbye for six weeks minimum with N'Golo. Then it is red cards -- for [Koulibaly], for Conor, then Ruben [Loftus-Cheek] is off injured and Mateo Kovacic is injured since eight weeks. He makes pre-season injured. This is what it reminds me.
"Reece James is off for the game today with illness. It is key player after key player, which has this effect. With our demands and the ambition we have, it is simply like that. But more important, if these key players are missing, you need to show a different mentality.
"It is not enough at the moment to win at Leeds and Southampton. There is no shame in it. We are humble enough to accept we can lose football matches. We hate it. But it is too easy to push us off the track, it is too easy to win challenges, it is too easy to bully us."
Asked to explain both goals, the first of which came from a poorly defended corner and the second a sweeping Southampton move which cut through the heart of Chelsea's team, Tuchel said: "Soft defending. What stops that? Pure mentality. Stop it with defending mentality.
"There is no superiority with the performance, there is no need to give shots away. There is no need. Just toughen up as a team and show a different mentality, that is today my assessment.
"I don't like to talk about it normally because you cannot prove it with data, like a body position or a tactical position in the field. but it is like this. Both goals are cheap goals and soft goals and should not happen if you expect to win a Premier League match in the evening in an away stadium. You need to be tougher than that."