The German shot stopper has been one of Arsenal’s shining lights in an otherwise turbulent 2019/2020 season.
But the former Bayer Leverkusen goalkeeper failed to get hold of Mason Mount’s 83rd minute free kick, allowing Jorginho the simplest of tasks to caress the ball into an empty net.
Chelsea took all three points to Stamford Bridge four minutes later after Tammy Abraham’s shot went through Leno’s legs.
The result ensured that Arsenal, who were so close to victory in Arteta’s first game in charge, ended up on the losing side, slipping to 12th place on the league table.
Arteta has however refused to blame Leno for allowing Chelsea a pathway into the game, instead focusing on how to rouse him from the disappointment.
"He will be down, but we have to lift him," Arteta said of Leno. "He's been brilliant for this football club.
"I'm really disappointed with the result, the way we conceded and the timing. I'm pleased with lots of things, but I'm disappointed to lose.
"I thought the structure was good. We need to control those situations but they are really good in transition.
"We have to move on."
Arsenal will have another chance to put things right when Manchester United come visiting on New Year’s Day.
The Gunners earned a 1-1 draw at Old Trafford in the reverse fixture earlier in the season but will be aiming for all three points in front of their home fans this time round.
