Rahul (unbeaten 93 from 53 balls) partnered Tristian Stubbs (38 from 23 balls) to take DC home after captain Axar Patel was sent back to the hut for 15 by Suyash Sharma.
Rahul and Stubbs added 111 for the fifth wicket with the former amassing most of the runs dampening RCB's hope.
RCB with the bat started to slide soon after Welsh cricketer Phil Salt started his business in an absolute hurry.
Until he was run out followed by Virat Kohli's fall, Salt slammed 37 from 17 balls in a huge boost to RCB's modest total of 163-7 in 20 overs.
Scores in brief
RCB 163-7 in 20 overs (Salt 37, Kuldeep Yadav 2/17)
DC 169-4 in 17.5 overs (Rahul 93*, Bhuvneshwar Kumar 2/26)