Potter admits Chelsea ‘lacked quality’ after third successive defeat
Joe Willock’s goal midway through the second half made it three consecutive defeats for Chelsea.
The Blues, beaten in four of their past five matches, are seventh in the table, seven points behind fourth-placed Tottenham.
Miguel Almiron dribbled across the edge of the Chelsea box and Willock steered a superb first-time strike beyond keeper Edouard Mendy and into the corner of the net.
The result continues a difficult spell for Blues boss Graham Potter, who admitted: “We lacked a bit of quality and there were too many unforced errors.
“In a game of not too many chances, they get the winner and then as much as we pushed, it wasn’t enough.”
Captain Cesar Azpilicueta picked up a calf injury and could be a doubt for the World Cup.
“I’m not sure where it leaves him with Spain,” Potter admitted.
Chelsea: Mendy, Azpilicueta (Pulisic 45), Koulibaly, Chalobah, Hall (Cucurella 74), Kovacic, Loftus-Cheek (Silva 7), Jorginho, Gallagher, Mount (Ziyech 73), Broja (Havertz 73).
Subs not used: Bettinelli, Silva, Aubameyang, Zakaria, Hutchinson.