"From a bowling perspective, we have lacked penetration. We have to get them two or three down in the powerplay. Always feels like we are on the back foot after the first four overs," Du Plessis said after seven-wicket loss to MI.
Du Plessis feels RCB were few runs short of a winning score as the dew played a big part in the second innings.
"Very tough pill to swallow. It was very wet out there, it will be nice to win a toss somehow. Credit to MI how they came out and made our bowlers make a lot of mistakes. Anyone that came in and found the middle of the bat.
"We spoke about it (dew). We knew the dew would play a big part. We needed 215-220. 190 wasn't enough. It is a big thing at some venues. When the dew settles in, it was very tough. We changed the ball many times. It is the only sport where the changes in conditions make a difference," he added.
Asked about Jasprit Bumrah's (5/21) terrific last spell, where he scalped four wickets, Du Plessis said: "He has been the difference in the two innings. We put them under pressure but the one guy, being out there myself, and you see him with the ball in his hand.
"You want to put him under pressure, but the variety does everyone in. He has got a really good bouncer, slower ball. Someone like (Lasith) Malinga was the best bowler in T20 cricket, but Bumrah has taken over the reins.
"You know you can bring him on and take the wickets but also be defensive."
The winning captain Hardik Pandya was also in awe of Bumrah's performance.
"I am lucky to have Bumrah in my side. He does this over and over again and every time I ask him and he gets the wickets. He practices in the nets. He has so much experience and the confidence," he said.
He also lauded the effort of Suryakumar Yadav, who struck 52 off just 19 balls in the pursuit of 197-run target to make life easy for MI.
"I did tell him (Yafav), welcome back when he scored the fifty. I have been opposition captain to him as well. Some place he hits, I have never seen any batter hit him. Whatever the situation requires," Pandya said.
The MI skipper also said their motive was to chase down the target quickly to better their net run rate.