Arteta made the bold decision not to start undisputed first choice goalkeeper David Raya in the biggest game of Arsenal’s season so far.
Arrizabalaga, who joined from Chelsea last summer, has been Arsenal’s cup ‘keeper all season, but struggled against Man City.
Rayan Cherki’s cross slipped through the 31-year-old’s gloves, allowing Nico O’Reilly to open the scoring.
Speaking to BBC 5 Live after the game, Arteta stood by his decision to play Kepa, saying: "I made a decision before the game based on what he has done all season, the fact he has played in the competition and helped us be where we are today.
“It would have been very unfair to choose a different one."
He later reaffirmed his stance when asked by Sky Sports, saying: "I would do it again. he deserved to play this game and has been phenomenal for us.
“Errors are part of football any anyone can make them."