I didn't underestimated CSK, most who watched the batting of RCB could've had the same feelings of mine.
Yes, with the scoring in much faster manner this is all unexpected. RCB reached 100 runs in 50 balls, and 150 runs in 80 balls. Further the team missed the momentum as the wickets of du Plessis and Maxwell fell. Even after that Dinesh Karthik made his contribution. Somehow this is the Dhoni's luck that brought him the win.
The way Royal Challengers were playing against Chennai Super Kings, they had a chance to win but in such circumstances every ball mattered and Royal Challengers Bangalore went towards the end. A few wickets here would have changed the outcome of the match. Again if the 7th and 8th no. players had been able to increase their strike rates they would have easily won the match. The game was excellent for both of the team. I don't want to blame anyone for the performance of the last match. It can be said that luck was not in favor of Royal Challengers Bangalore.