After opting to bat first, contrary to their blazing starts in the earlier matches, CSK started off in a circumspect manner against Rajasthan Royals and lost Dwayne Smith early for six runs.
Chris Morris then removed Suresh Raina for three runs in the fourth over to hand his team the early advantage.
Brendon McCullum struggled to time the ball well early on but overcame the tough period and scored his fifty off 44 balls and along with Faf du Plessis, steadied the CSK innings.
Faf du Plessis (28) combined for a 101-run stand for the third wicket, but he was unfortunately run-out at the non-strikers' end in the 17th over.
Brendon McCullum scored 81 off 61 balls before perishing to Chris Morris in the 18th over as CSK went on to post 157 for 5.
In chase of 158, Ajinkya Rahane started aggressively scoring 23 off 17 balls but was surprised by a Mohit Sharma bouncer and perished in the sixth over.
Ravindra Jadeja removed Steve Smith cheaply for four and went on to take two more wickets to leave Rajasthan Royals reeling.
Dwayne Bravo plucked one out of thin air to remove Shane Watson for 28.
Ravindra Jadeja went on to scalp his fourth wicket of the night and finished with enviable figures of 4-0-11-4.
Sanju Samson kept his team alive with a 17-ball 26-run knock but got out to Dwayne Bravo in the 18th over.
CSK restricted Rajasthan Royals to 145 for 9 and registered a 12-run win to become the first team to qualify for play-offs this season.