The Argentina legend has criticized the Real Madrid goalkeeper following his nightmare showing on Friday night.
The goalkeeper was at fault for at least one of the goals as the reigning world and European champion suffered a shock thrashing at the hands of Louis van Gaal's Oranje.
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He has since accepted the blame for the defeat, and Argentina legend Maradona says the performance shows Mourinho was right to favor Diego Lopez over the 33-year-old.
"He had the worst game I've ever seen in my life...and it reminds me of what my friend Mourinho told everyone about him," the 53-year-old told Telesur. "He said Casillas wasn't the right keeper and he paid for that. He had to leave, but in the end it turns out that Mourinho was right."
Sergio Ramos was also criticized in the aftermath of the game and Maradona felt the Madrid center back lacked in pace against Arjen Robben.
"He beat him in a race coming from five meters behind," he added.
Casillas and Ramos will hope to make amends when they face Chile in their next Group B clash on Wednesday night.