The last time Mertesacker faced the 25-goal Chelsea striker, he was sent off for bringing him down as Arsenal lost 1-0 at the Emirates in January last year.
Arsene Wenger accused Costa of conning the referee that day but Mertesacker insists he will not let it happen again in today’s FA Cup final.
The 32-year-old is set for his first start in over a year as Laurent Koscielny is banned and Shkodran Mustafi touch and go after suffering concussion.
Mertesacker, who is expected to captain the team today, said: “He is one of the main threats. He knows what he is doing.
Per Mertesacker insists he won't make the same mistake against Diego Costa again
Per Mertesacker was shown a red card the last time he faced off against Diego Costa
“Especially in the box, he is a scoring machine. But I won’t do that on my own. I think we need to turn up as a team, no matter what happens.
“There is so much in the past, I have forgotten about what happened with him. You cannot think about it. You have to learn from mistakes.
“I try to think about what went wrong, open myself to criticism, but face the next day and be intelligent enough to cope with another situation when it comes.”
Mertesacker had surgery on a knee injury he suffered in a friendly last July and only made his first appearance of the season off the bench against Everton last weekend.
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1. Too. many. plastic. flags.
He has been training since February but has not even played any reserve team football, and knows he will have his work cut out keeping Costa quiet.
But he has vowed to repay Arsenal’s faith in him after the club exercised an option to extend his contract by a year while he was still injured, just before Christmas.
“The manager backed me up, made me captain, knowing I was going to be sidelined for more than six months,” said Mertesacker. “I’m grateful, so I want to make sure I try to give something back.”