Manchester City's Premier League title defence fell apart at the seams in a 3-1 defeat at Southampton when goalkeeper Joe Hart committed a howler and Gareth Barry scored a bizarre own goal.
Manchester United can increase their lead over City at the top to 12 points with 12 games left if they win at home to Everton on Sunday after coach Mauricio Pochettino sealed his first win for 15th-placed Southampton.
First Barry lost the ball in midfield after seven minutes and Jason Puncheon stormed forward before coolly finishing off a rebound after Hart's sprawling stop.
Hart, who saved a Ronaldinho penalty during an excellent display for England in a friendly against Brazil on Wednesday, then inexplicably let a Rickie Lambert shot go through his legs and Steven Davis slid the ball in midway though the first period.
Edin Dzeko replied for City after a quick counter attack but just after the break, a weak cross came in and Barry decided to pass the ball back to Hart only to send it into the corner of the net with the keeper beaten.
The unstoppable Gareth Bale earlier scored twice in Tottenham Hotspur's 2-1 home victory over Newcastle United while rivals Chelsea and Arsenal also won to add spice to the race for the Champions League spots.