Tamil Nadu ended the day at 332 for 2, a lead of 74 runs in response to Tripura's 258 riding on Sundar's maiden first-class ton which included 14 fours and one six. He has batted for 223 balls so far.
Washington Sundar opened for Tamil Nadu in place of Murali Vijay, who is sitting out the game due to a neck spasm.
Earlier, the home team wrapped up the Tripura innings for the addition of just 14 runs to the overnight score of 244 for 7.
K Vignesh took two of the three wickets to fall to finish with four for 41. R Ashwin got the other to finish with two wickets for 64.
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It took all of 6.1 overs for TN to polish off the visitors' tail.
Tamil Nadu began their reply in a positive manner with Mukund and the young Sundar scoring briskly. The two left-handers took the attack to the Tripura bowlers and took advantage of some pedestrian stuff.
While the TN captain played some beautiful shots on the off-sider, the lanky Sundar blossomed after a cautious start and hit strokes around the wicket.
The two openers went on the offensive in the post-lunch session and at one point hammered 32 runs in three overs. Sundar hammered Tripura skipper Mani Shankar Mura Singh for three boundaries in one over.
Just when it appeared that the two southpaws would carve out big individual scores, Mukund fell to a catch by Gurinder Singh in the point region off Joydeep Bhattacharjee, making his debut.
Sundar and Indrajith continued to make light of the inconsistent Tripura attack and put on 152 runs in 216 balls to put the home team in the driving seat.
Indrajith batted efficiently and proved the perfect foil for Sundar, who was constantly on the lookout for runs.
Mura Singh told reporters at the end of the day that the bowlers were inconsistent and admitted that Tamil Nadu batted well.
Washington Sundar said he was happy to get the ton and looked to carry on the good work tomorrow.
At Vadodara: Baroda 373 all out in 128 overs (Swapnil Singh 88, A Sheth 70 not out, Vishnu Solanki 61, B Ayyappa 4 for 69) vs Andhra Pradesh 190 for 2 in 46 overs (G Hanuma Vihari 71 batting, Ricky Bhui 53 batting, K S Bharat 40).
At Indore: Madhya Pradesh 409 in 144.3 overs (Naman Ojha 180, Ankit Sharma 67, Akash Parkar 4 for 70) vs Mumbai 130 for 1 in 33 overs (Jay Bista 89 batting).