Trevor Chalobah opened the scoring for the Blues, who then had two further goals disallowed before James Ward-Prowse’s penalty put Saints on terms but the midfielder was subsequently shown red card and the home side made their man advantage pay.
After back-to-back defeats, against Man City and Juventus, Thomas Tuchel made five changes to his side and two of them combined to open the scoring as Chalobah steered home from Ruben Loftus-Cheek’s flick on.
Romelu Lukaku then had a goal ruled out for offside before Werner saw his effort chalked off in much more controversial fashion, VAR pulling the play back for a foul by Cesar Azpilicueta much earlier in the build-up.
Former Blues academy youngster Tino Livramento drew a rash challenge from Chilwell to earn a spot-kick which Ward-Prowse stepped up to convert but the Englishman was soon on his way as his yellow card for a late tackle on substitute Jorginho was upgraded to red following a VAR review.
Werner then put the Blues back in front from close-range five minutes from time, before Chilwell made amends for conceding the penalty with a terrific volley that Alex McCarthy just failed to claw away after Lukaku and Azpilicueta had both hit the woodwork.