Al-Johar was devastated after Saudi's 8-0 drubbing to Germany in their opening match in Group E.
But his side played with character and were unlucky not to score in limiting the Africa champions to a single goal from Samuel Eto'o on 65 minutes.
And despite no chance of qualifying for the second round, Al-Johar insisted his side would play to their full potential in their final match against Ireland on 11 June.
Today we showed more the real picture of the Saudi team
Saudi Arabia coach Nasser Al-Johar
"In the first match we were all shocked and I would like to apologize to our officials and fans," said Al-Johar.
"But today we showed more the real picture of the Saudi team.
"The Cameroon team are one of the favourites of the cup and have a great chance of going through to the next round.
"We promise to do our best in our final match and say goodbye to the World Cup with a good picture."
Saudi will be playing for pride in Yokohama, while Ireland will know that a 2-0 victory would ensure progression from the group.
They would qualify on goal difference, irrespective of the result between Germany and Cameroon.