The 27-year-old has 183 runs in three matches and he attributed his form to the good domestic season he had coming into the tournament.
"This whole year has been good for me. I had a good domestic season and it is important that you carry forward that momentum into Twenty20 cricket. I am very confident that given a chance at any level, I will be able to do the best I can, so I am just motivated enough to get runs on the board," he said.
Mumbai lost their openers -- batting stalwarts Ricky Ponting and Sachin Tendulkar -- with just a run on the board, but Karthik (86) shared a 132-run stand with Rohit Sharma (74 not out) to propel the side to a massive 209 for 5.
"If you see the team's context, every knock is important considering we were no less than one for two and it was important that Rohit and I put up a big partnership and the way he batted was just beautiful. He was giving me the strike when I required it and towards the end, he hit the big shots after I got out," he added.