Che Adams equalised for Saints after a defensive mix-up between Kepa Arrizabalaga and Kurt Zouma, only for Havertz to put Chelsea back in front.

The Germany midfielder's first league goal for the Blues could not win the day however, as Jannik Vestergaard's added-time effort forced a draw at Stamford Bridge.

"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."

Chelsea must move quickly onto Tuesday's Champions League opener against Europa League champions Sevilla at Stamford Bridge, with boss Frank Lampard aware of the scale of improvements required.

The Blues boss has maintained however that formation switches are not to blame for Chelsea's leaky defence.

"I don't think it's conceding goals in relation to the shape of the team, that's something for me to think about all the time," said Lampard.

"I'm not dead-set on playing that formation, there were loads of great things from the 4-2-3-1.

"But it is something we need to continue working on, because it is a change."

Saints' last-gasp goalscorer Vestergaard insisted Ralph Hasenhuttl's side were full value for their point in west London.

"It was challenging, a high-paced game; they came at us fast and often," he told Southampton's official club website.

"We deserved to be down and had to fight our way back into the game.

"It's difficult to come back from such situations, but that we did is massive.

"Based on the second-half the draw was deserved."