Skipper Vijay Shankar returned to the side after missing the first two games owing to injury concerns, but couldn't do much with the bat, falling for four to Amogh Desai.
Electing to bat after winning the toss, Tamil Nadu lost M S Washington Sundar (14) at 29, not before he had hit two boundaries and a six.
Karthik, who has been in superb form, got into the act quickly and hit shots all round the wicket. He smashed six fours and a sixer before falling in the 15th over.
Though Abhinav Mukund (12) and Shankar fell in quick succession, Karthik found an able partner in B Aparajith (26). The two added 54 runs in just about seven overs.
Some lusty blows by R Sanjay Yadav (28 not out, 20 balls, 1X4, 2X6) and N Jagadeesan (10 not out, 1X6) helped swell the total to 155.
Goa's chase was stifled by the loss of wickets at regular intervals with none of the batsmen being able to get a big score. Skipper Sagun Kamat made the top-score of 41 but tight bowling by the Tamil Nadu bowlers made things difficult.
Leg-spinner M Ashwin, who kept things tight in the middle along with offie Washington Sundar, picked up two wickets each while left-arm spinner R Sai Kishore bowled just one over to scalp one victim.
Medium-pacers K Vignesh and Athisayaraj Davidson got a wicket apiece.
Brief scores: Tamil Nadu 155 for 5 in 20 overs (Dinesh Karthik 56, Sanjay Yadav 28 not out, Amogh Desai 3 for 22) beat Goa 130 for 7 in 20 overs (Sagun Kamat 41, M Ashwin 2 for 22, Washington Sundar 2 for 20). Points: TN: 4; Goa: 0.
At Visakhapatnam: Karnataka 205 for 5 in 20 overs (Karun Nair 77, K Gowtham 57, Ravi Kiran 2 for 33) beat Hyderabad 203 for 9 in 20 overs (Akshath Reddy 70, Tanmay Agarwal 38, Bavanaka Sandeep 34, Stuart Binny 3 for 29). Points: Karnataka: 4; Hyderabad: 0.
Kerala 120 all out in 12 overs (Vishnu Vinod 45, Sanju Samson 32, M Harishankar Reddy 4 for 2, Bandaru Ayyappa 3 for 32) lost to Andhra 126 for 4 in 13 overs (Ashwin Hebbar 64, G H Vihari 25, Basil Thampi 2 for 35). Points: Andhra: 4; Kerala: 0.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)