Southampton delivered a severe blow to Manchester City’s Premier League title defense by beating the champions 3-1 after mistakes by Joe Hart and Gareth Barry.

Jason Puncheon put Southampton ahead after seven minutes and then Rickie Lambert’s fierce drive squirmed through the grasp of goalkeeper Hart, allowing Steven Davis to bundle in the second.

Edin Dzeko reduced the deficit as half-time approached, but a two-goal lead was restored early in the second half when Barry passed into his own goal unchallenged.

City manager Roberto Mancini said: “I think it’s our worst game in the last two or three years.”

Already nine points behind Manchester United, the gap could be 12 points if the leaders beat Everton on Sunday.