Raheem Sterling opened the scoring at St Mary’s but the visitors had no response to goals from Romeo Lavia and Adam Armstrong.
Tuchel is concerned about the mentality of his players in a defeat which would have seen a more emphatic scoreline without the goal clearances of Marc Cucurella and Thiago Silva.
“We are not strong enough to win these away games at the moment,” Tuchel said at Southampton. “It was the same story at Leeds. At Leeds we thought the problem was that we didn’t score in the first 25 minutes, and they knocked us off balance with two goals and we didn’t find no answer.
“Today we scored, everything was fine, but a set piece again, a sloppy defense again, and we were off balance. We didn’t react. We were lucky not to take any third goal early in the second half and we weren’t strong enough as a team to react.
“It’s soft, soft, soft in defense. What stops that? Pure mentality. You stop it with a pure mentality, a defense mentality so that there is no superiority for the opponent, you just have to toughen up as a team.
“I don’t like to talk about it normally because you can’t prove it with data or body position, but that’s how it is. Both goals are easy goals and shouldn’t happen if you want to win. a Premier League game. You have to be tougher than that.”
Chelsea’s fitness concerns grew ahead of the game. Reece James was ruled out with illness and joined Trevoh Chalobah, who suffered an ankle injury, on the sidelines.
James’s replacement on the night, Ruben Loftus-Cheek, limped off at half-time and added to a longer-term injury for N’Golo Kante and a suspension for Conor Gallagher.
“It reminds me of Juventus last season,” Tuchel said of the recent injury spate. “We played a fantastic game at Stamford Bridge, and after that we had Chilly for eight months and Kante for eight weeks.
“It was the same against Tottenham this season. We had a fantastic performance and after that our key player said goodbye for six weeks minimum, then it’s the red cards, and Ruben is injured and Reece is ill.
“It’s key player after key player. But more importantly, if these key players are missing, we need to show a different mentality. It is not enough at the moment to win at Leeds and Southampton.
“We are humble enough to know that we can lose football games, although we hate it, but it’s too easy to push us off the track.”
“There is such a thin line between apologies and explanations,” he added. “I don’t want to go down that road and give anybody room for an apology.
“Closing the transfer window will help. We will know who is fully committed and what role each must play and fulfill, and everyone, including me, must increase their level of performance. This is a good performance, not a disaster. , but that is never enough.