The France stopper had started the game but was substituted in the closing stages of extra-time before hailing the team success for the Blues.
Hakim Ziyech had put the Champions League holders ahead only be be forced off with a shoulder injury as Gerard Moreno's leveller saw the game finish 1-1 after extra-time.
Chelsea boss Thomas Tuchel had Arrizabalaga stripped and ready to come on in the final seconds, explaining afterwards that it was a statistical decision made after pouring over 1000s of penalties taken against his goalkeepers.
Mendy left the field promptly and without complaint - unlike Arrizabalaga, who seemingly refused to be substituted in a similar situation in a Carabao Cup final in 2019 - and was happy to see his colleague save twice to secure the Super Cup.
"We work for this success," Mendy told chelseafc.com.
"I knew since last season that if Kepa came on the pitch he would help the team like he did. I am really happy for Kepa.
"This is teamwork, it's a team effort. When you play for Chelsea you play for success, you play for titles. We did it together and we are happy."
Arrizabalaga was full of praise for Mendy, who had made a number of key saves to keep out Villarreal - the Europa League holders also hitting the woodwork twice in normal time.
"It's not a typical situation," said the Spain goalkeeper.
"I was ready because I knew this could happen, and I tried to be ready mentally and physically when we arrived at penalties.
"Edou did a fantastic job before, it was a tough, tough game against a very difficult team.
"We won and we are so happy. All the team did a fantastic job and we have the medal."