The Gunners came from a goal down to beat last season's champions 4-2 on penalties, securing their first final appearance since 2005.
The manager told the club's official website: "It was important to start well and our keeper got us on the confidence level in a very good way. After that we took it in a very professional and calm way.
"We needed spirit and nerve. We have shown both I think because we were 1-0 down, we came back and we couldn't score the second goal. But overall we were spirit-wise and on the nervous front at the expected level.
"We needed to be absolutely strong on the mental front and I'm happy that we have responded like that because we have been questioned on that front."
Arsenal will face either Hull City or Sheffield United in the final next month.