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.
You can love or hate Mahendra Singh Dhoni. But you can't deny the fact that he is the best captain out of all during this season of the Indian Premier League. It was his tactics which brought the victory to Chennai Super Kings. And trust me, it was not an easy task to defend the target against star batsmen such as Virat Kohli, Faf du Plessis and Glenn Maxwell. They are some of the best in T20 format. And on the other hand, CSK had some inexperienced bowlers, in the form of Akash Singh, Tushar Deshpande and Matheesha Pathirana. Without MSD, they would have lost the match yesterday.