Chelsea were two goals to the good at Stamford Bridge, but were pegged back to 2-2 with Southampton’s second goal a mistake between Kurt Zouma and Kepa Arrizabalaga.
Havertz had Chelsea back in front, but Jannik Vestergaard’s injury-time goal sealed a late draw for the Saints – the second 3-3 draw in three Premier League games for Frank Lampard’s men.
Havertz shouldered the blame for Saints’ first goal, admitting losing possession for Danny Ings’ smart finish “changed the game”.
“We’re very frustrated about the result,” Havertz told Chelsea’s official club website.
“We had 42 good minutes in the first-half but then I made a mistake and we conceded a goal, which changed the game a little bit.
“We got it to 3-2 and then we had to take the result and get the win at home but we didn’t do it.
“Now we have to stick together and hopefully we can do better next time.
“We have to take responsibility for that; we have 11 players on the pitch and everybody has to work hard so we don’t concede goals like this.
“It’s not always one person who makes the mistake so we have to look at our mistakes and try to solve the problems.
“It would have been great if my goal was the winner. Of course, I’m happy with that but very frustrated too about the result.
“We had to take these three points at home and we can do that so it was a bad day for us.”
Additional reporting by PA.