Werner was speaking after he scored a brace in Chelsea's 3-3 draw with Southampton, another game which saw Frank Lampard's side drop points as a result of errors at the back.
"In Germany we always say defence wins titles," Werner said after the game. "If we concede so many it is hard to win games and win titles."
He added: "The first half we played very well. When you get a goal two or three minutes before half-time it is not easy. You have to think with a clear head.
"Southampton make a lot of pressure on us and pressed us high. We gave them too much in terms of opportunities. We have to win the game.
"I am happy about the goals but I want to win the game. 50% I am happy, 50% not.
"I don't know if we have a problem but the last three games we concede six goals and it is not where we want to be, to compete for titles."
Lampard was also unhappy with the result, telling BBC Sport: "You go two goals up you want to finish it off. It was the best we've played this season for sure at this stage.
"But Southampton are a good side. They put pressure on us off the ball. They put us under pressure after the first goal. My message at half-time was that the goal shouldn't change too much.
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"We never got to the same levels in the second half. We can do better. They are great goals [from Werner]. The second in terms of the team was class but it is a lot to do by Timo.
"Those moments will come from him and other players. But we need to be more solid and making individual mistakes gives other teams chances."