B Indrajith scored an unbeaten ton to lead Tamil Nadu's fightback as the team finished day two at 239 for 5 in response to Mumbai's 374 in a Ranji Trophy Group "C" match at Sharad Pawar Cricket Academy BKC.
Indrajith (105 batting) and young all-rounder M S Washington Sundar (69) rescued Tamil Nadu from a rather precarious 69 for 4 with a partnership of 157 runs.
Earlier, resuming at the overnight score of 314 for 7, the home side added 60 to its total with the Akash Parkar (33 not out) and Aditya S Dhumal (13) putting on 35 crucial runs for the 10th wicket.
Vijay Shankar was the most successful Tamil Nadu bowler, finishing with 4 for 52 while the country's premier off-spinner Ravichandran Ashwin had figures of 3 for 78.
The Tamil Nadu reply saw skipper Abhinav Mukund fall early when he was bowled by Akash Parkar for just 9. The stylish Murali Vijay, who has been recalled to the India Test side to face Sri Lanka next month, was caught behind by Aditya Tare of Vijay Gohil for 11.
One-drop batsman M Kaushik Gandhi, who hasn't got going this season so far after a prolific run in the 2016-'17 season, didn't last too long and was castled by Nayar for 6.
All-rounder Vijay Shankar, who replaced Gandhi, adopted a positive approach and cracked four boundaries. He was stumped by Tare off Gohil for 18 to end a promising association with vice-captain Indrajith.
With the top four gone for 69, Tamil Nadu looked in trouble when Indrajith and Sundar came together for a fruitful partnership.
Sundar, who hammered 159 in the previous game against Tripura, played with a lot of enterprises and kept the scoreboard moving with some handsome shots. He used his feet to the spinners and played the fast bowlers with a degree of ease.
The lanky southpaw grew in confidence in the company of Indrajith and the two got runs fluently. Sundar hit 11 fours and a six before becoming Dhawal Kulkarni's first victim.
Indrajith, who has so far faced 173 balls and struck 12 fours, and Ashwin ensured that there were no further setbacks for the visitors before the close of play.
Brief scores: Mumbai 374 all out in 103.1 overs (Prithvi Shaw 123, Vijay Shankar 4 for 52, R Ashwin 3 fo 78) vs Tamil Nadu 239 for 5 in 65 overs (B Indrajith 105 batting, M S Washington Sundar 69, Vijay Gohil 2 for 58).
At Vizianagaram: Andhra Pradesh 584 for 4 declared in 166 overs (G Hanuma Vihari 302 not out, D B Prashanth Kumar 127, Ricky Bhui 100) vs Odisha 32 for 1 in 12 overs.
At Agartala: Tripura 205 all out 64.2 overs (B B Ghosh 65, Gurinder Singh 57, Ishwar Pandey 3 for 40, Ankit Sharma 3 for 61) vs Madhya Pradesh 201 for 7 in 66 overs (Rajat Patidar 79, Harpreet Singh Bhatia 70, M B Mura Singh 2 for 14).