The visitors still trail the hosts by 92 runs with five wickets in hands and they would be eyeing a first innings lead tomorrow to ensure a point even if the match peters out to a draw.
Tanmay was batting on 72 off 166 balls, which included 10 hits to the fence and he found a belligerent partner in Praveen, who thrived on the largess of the butterfinger Delhi players and was unbeaten on 54 off 72 balls and he made Delhi pay for the dropped chances by hitting five boundaries and three sixes in his entertaining innings.
Uttar Pradesh began on a shaky note as Ishan Sharma (2/51) drew the first blood by removing opener Shivkant Shukla (8) and Ashish Nehra's twin blows, Rohit Prakash (39) and Ravikant Shukla (0) reduced the visitors to 79 for three.
Ishan and Chetanya Nanda tightened the noose and removed Rizwan shamsad (4) and Jyoti Yadav (16) to leave the visitors gasping at 125 for five.
But the noose had a loose end and it was Delhi's fielding which let the hosts down.
Rahul Sanghvi squandered a caught and bowled chance when Praveen was at 18 and the batsman later responded with successive sixes off the spinner to reach his fifty and Rajat Bhatia then floored the batsman when he was batting on 51.
Tanmay took 106 balls to reach his fifty and the youngster played a sedate knock to take his side to 207 for five when bad light forced curtain on today's proceedings nine overs before the schedule.
'It was a satisfying knock on my Ranji debut and we would like to bat as long as we can tomorrow. The immediate target would be to take a first innings lead,'' Tanmay later said.
Earlier, Delhi resumed on their overnight score of 258 for seven but could add only 41 runs before their innings folded up.
The highlight of the Delhi innings was Aakash Chopra's marathon knock of 150, which came in 437 minutes, during which he faced 311 balls and hit 15 boundaries.
''I thought we would push it a bit more but that was not to be,'' lamented Delhi captain Mithun Manhas.
''And our fielding also let us down. Praveen got life on two occasions, otherwise they would have been seven down and we could have been in a better position.
''Anyway, the ball is doing a bit in the morning and we are hoping to polish off the tail early tomorrow to get a first innings lead,'' Manhas added.
Delhi 299 all out (Akash Chopra 150, Viraat Kohli 42, Rajat Bhatia 32; Praveen Kumar 4 for 62, Piyush Chawla 2 for 64, R P Singh 2 for 96) Vs Uttar Pradesh 207 for 5 (Tanmay Srivastava 72 n o, Praveen Kumar 54 n o Rohit Prakash 39; Ashish Nehra 2 for 76, Ishan Sharma 2 for 51)