The Swansea goalkeeper put in a phenomenal performance as Arsenal crashed to a 1-0 home defeat.
Arsenal boss Arsene Wenger was frustrated with his side's inability to put the ball past a stubborn Swansea City side, as the Londoners suffered a second league defeat to the Welsh outfit courtesy of a superb performance by a familiar face.
The Poland international spent seven years at Arsenal, without ever really managing to claim a first team spot, and was released last summer after helping the Londoners win the FA Cup at Wembley.
After moving to Swansea on a free transfer, the 30-year-old returned to haunt his former employers on his first return to the Emirates, making 9 saves to stop Arsenal from scoring.
"It’s frustrating because we lose a game when we have no threat to concede a goal," Wenger told Sky.
"Fabianski had a great performance, but that’s sometimes the case [when a player returns to his old club].
"Sometimes our finishing made it a bit easier for him."
Despite the loss, Wenger thought his side played well, with the quality of Fabianski the only thing stopping Arsenal from a convincing win.
"You have to learn from defeat but you can take encouragement from a defeat like that," he added. "There’s a lot of positives as well.
"These kinds of games you play 20 and you win 19, but this was number 20."