NILS-Eric Johansson admitted he may have made contact with Teddy Sheringham.
Spurs protested loudly for a penalty in the dying minutes after Nissa's challenge on the Tottenham favourite.
"My first reaction was that he dived," said Johansson. "I can't say if it's a penalty or not, but the referee said it wasn't so that is that.
"It was hard in the later stages as we had to focus on every ball and they had a lot of players in the box but we kept organised and tried to stay cool.
"As for Brad, I thought he was phenomenal. He saved us as he has done a few times before this season. He deserved the man of the match award."
Johansson had never tasted Cup success before so he was quick to label Rovers' victory as the high point of his career.
"This is the highlight of my career without a doubt. It's amazing. Winning cups and playing in unbelievable stadiums like Cardiff is all part of football.
"I also thought the fans were amazing. They helped us a lot."
Now the Swede is backing Rovers to stay in the Premiership - starting with a victory at Bolton on Saturday.
"They are all big games now and this is good for our confidence.
"I think we will make it. We have the team to stay in the Premier League.
"We know on a good day we can match any team."
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