South Africa's Dewald Brevis hit a 22-ball fifty as Chennai Super Kings beat Kolkata Knight Riders by two wickets on Wednesday, leaving the defending IPL champions in grave danger of missing the playoffs.

Chasing 180 for victory, Chennai slipped to 60-5 in the sixth over before Brevis hit 52 and impact substitute Shivam Dube made 45 to steer the team home with two balls to spare at Kolkata's Eden Gardens.

Skipper M.S. Dhoni hit a six when Chennai needed eight off the last over and finished unbeaten on 17 with number 10 Anshul Kamboj hitting the winning four off Andre Russell.

The result left Kolkata's chances of making the playoffs hanging by a thread as they need to win their remaining two matches and hope other results go their way.

Five-time champions Chennai had already bowed out of the playoff race.

Afghanistan spinner Noor Ahmad set up victory with his four wickets that kept Kolkata down to 179-6.

In reply, Chennai openers Ayush Mhatre and Devon Conway both fell for a duck but IPL debutant Urvil Patel clobbered the Kolkata attack in his 11-ball 31.

Spinner Varun Chakravarthy bowled Ravindra Jadeja but Brevis and Dube put the chase back on track in their carefully crafted stand.

Brevis took his time to get going before he blasted 30 runs off Vaibhav Arora, reaching his fifty with three sixes and three fours in one over.

Chakravarthy soon cut short Brevis' blitz, but the left-handed Dube then found Dhoni for company and the two chugged along.

Arora dismissed Dube as Rinku Singh clung on to a steepling catch before taking another opportunity to dismiss Noor, but Dhoni and Kamboj got the team through to just their third win in 12 matches.

Earlier Kolkata lost opener Rahmanullah Gurbaz early on 11 before Sunil Narine (26) and skipper Ajinkya Rahane, who made 48, put on 58 runs to rebuild the innings.

Noor broke the stand with left-arm wrist spin to get Narine stumped by Dhoni and three balls later had Angkrish Raghuvanshi caught behind for one.

Rahane was joined by Manish Pandey but was denied his fifty by Jadeja's left-arm spin, spooning a reverse sweep to backward point.

Pandey stood firm and combined to add 46 runs with Russell, who hammered 38 off 21 balls before Noor struck again to have the big-hitter caught at long-off.

Noor removed Rinku for nine and despite Manish's presence Kolkata's total ultimately proved insufficient.