The Serbian international was at fault for both goals that the Welsh club scored that evening at Stamford Bridge, which has left his side's chances of reaching Wembley hanging in the balance.
Ahead of the second leg at Swansea's Liberty Stadium tonight, Ivanovic admitted that he had not put in a poorer performance than the one that he produced last time out.
"The first match was a very difficult game for us and for me it was probably my worst game for Chelsea," he told the London Evening Standard. "I apologised to everyone afterwards in the dressing room. That is normal, to admit you made a mistake, but you have to be mentally strong and mentally ready to forget these things.
"I was very disappointed but the good thing about football is that you always have tomorrow. I would like to play against Swansea to put things right, to stay focused and get the team to Wembley."
To advance through without the need of penalties, Chelsea must win by three clear goals this evening.