The Blues held a 2-1 advantage heading into the closing minutes of extra time when Malang Sarr made an error and subsequently conceded a penalty.
However, Arrizabalaga saved Ryan Hardie's spot kick, earning Chelsea a place in the last 16 of the FA Cup, but Michels wanted to praise the Spaniard's overall performance rather than focus on his late intervention.
Speaking to reporters, Michels said: "It's not only about the penalty, it's also about the performance. In the last matches, I've felt him very reliable in his game. His strength is to save penalties, he's shown it a few times now. In training it's hard to beat him and in penalty shootouts he has the ability to read the mind of what the player is going to do.
"We are very happy with Kepa and he deserves this trust because he is a fantastic guy. It is hard for him because Edou (Mendy) is playing very good, but Kepa is doing very good work and is an amazing guy. I am happy for him."