The 26-year-old, who joined Arsenal in the summer, made his first start in yesterday's 2-1 defeat to Southampton in the third round of the competition at the Emirates.
"I'm really happy to make my debut and play my first game with Arsenal," Ospina told the club's official website. "Unfortunately we didn't win and the result went against us but I just want to keep working. I'm really tranquil because I did my best.
"The second [Southampton goal] was superb and [Nathaniel] Clyne is a really skilful player. There were a lot of people in the box and when I saw the ball, it moved and I didn't have time to react.
"I felt really happy when I went onto the pitch because people were supporting me a lot. I'm learning all the time. The style in England is different because they play really quickly and with a lot of aerial balls."
Arsenal will now turn their attention to the Premier League when they take on North London rivals Tottenham Hotspur on Saturday.