Sunderland: Seven months after winning the Premier League with Manchester City, Adam Johnson inflicted a blow to his former club's title defence by clinching a 1-0 victory for Sunderland on Wednesday.
The England winger, who was considered surplus to requirements at City in the off season, embarrassed former teammate Joe Hart with a dipping strike in the 53rd minute that beat the goalkeeper at the near post.
The setback left second-place City seven points behind leader Manchester United at the season's halfway point.
Sunderland turned in one of their best displays of the season, with Hart having to turn away Steven Fletcher's skidding effort and keep out Stephane Sessegnon late on.
But Sunderland goalkeeper Simon Mignolet was also alert to deny Yaya Toure and David Silva before the break, and Sergio Aguero in the second half as City slumped to a third consecutive 1-0 loss at Sunderland.
City might have been ahead with just eight minutes gone. Captain Vincent Kompany's header came back off the crossbar and Yaya Toure's goalbound follow-up was hacked away by Mignolet.
In Norwich, Chelsea ended the hosts' five-game home unbeaten run with a solid if unspectacular 1-0 victory at Carrow Road.
Juan Mata scored the only goal of the game in the 38th minute when he placed a ball from Emboaba Oscar in the bottom right corner of Mark Bunn's goal.
Chelsea remain third in the table with 35 points, just four behind Manchester City in second with a game in hand.
Norwich, who saw their 10-game unbeaten run in the league come to an end against West Bromwich Albion on Saturday, drops to 11th with 25 points.