Sent into bat by the home side, Tripura was dealt an early blow when Bishal Singh nicked the very first ball from K Vignesh to wicket-keeper Dinesh Karthik. Udiyan Bose, who made a century in the rain-affected opening game against Odisha, fell to L Vignesh for 2 to leave the team at 18 for 2.
R D Banik and Patel added 23 runs before the former was bowled by Rahil Shah for 17.
Patel, who was part of the India team that won the Under-19 World Cup in 2012 and Singh played several attractive strokes in their 162-run partnership.
The 24-year-old Patel fell while going for a big hit off M S Washington Sundar's bowling and was well caught by J Kousik, one short of a well-deserved ton.
More From This Section
Abhijit Dey fell five runs later, trapped leg-before by Sundar for a duck.
Gurinder Singh fell in the 88th over as Tamil Nadu hit back towards the end of play after a tough second session.
For the host, K Vignesh and Sundar picked up two wickets each while Ashwin, L Vignesh and Shah got one scalp each.
Earlier, Tamil Nadu made three changes to the side that played Andhra Pradesh in the first game, bringing in Dinesh Karthik, J Kousik and handing a debut to left-arm spinner R Sai Kishore in place of Murali Vijay, B Aparajith and N Jagadeesan.
Further, he said Vijay was expected to be ready for the next game.
He said team had not maintained pressure after striking early blows, but gave credit to the Tripura batsmen.
"It is about maintaining the pressure. It is something we need to look into. It has happened for the second time. Maybe we are losing momentum during the break. Somehow, the focus seems to drift. Have to give credit to the (Tripura) batsmen, they played well," he said.
The TN coach praised Washington Sundar and said "he bowled really well."
Patel, on his part, said more than missing out on a century he felt it would have been better if he had been batting at the end of the day.
"The ball was there was to be hit. I don't regret it (going for the shot and getting out). I think I played really well the whole day. It feels bad to get out and get out on 99. It happens. I will try harder in the next innings," the Tripura right-hander said.
Brief scores - Group "C": Tripura 244 for 7 in 90 overs (Smit Patel 99, Yashpal Singh 96, K Vignesh 2 for 36, M S Washington Sundar 2 for 40) vs Tamil Nadu.
At Indore: Madhya Pradesh 250 for 5 in 89 overs (Naman Ojha 99 batting, Ankit Sharma 63 batting, Wasim Ahmed 40, Akash Parkar 2 for 48) vs Mumbai.
At Vadodara: Baroda 247 for 7 in 90 overs (Kedar Devdhar 93, Vishnu Solanki 60, Swapnil K Singh 30 batting, B Ayyappa 3 for 46) vs Andhra Pradesh.