Resuming on 115 for one, Uttar Pradesh could add just 91 runs to their overnight total, losing as many as nine wickets in only 34.4 overs on a day when only 51.4 overs could be bowled because of inclement weather.
Thakur wreaked havoc, taking three quick wickets in the morning to push the hosts on to the backfoot early on.
Although Thakur failed to complete a hat-trick, he also dismissed the other overnight batsman -- Tanmay Srivastava, who top scored with 67 off 206 balls.
The hosts could not recover from the initial damage and kept losing wickets at regular interval.
Eklavya Dwivedi (23) was the only other batsman, who could chip in with some runs.
Both the openers were dismissed by Amit Mishra (2/13).
At stumps, Hiken Shah was unbeaten on 14 and Suryakumar Yadav was yet to open his account.
Brief scores:
Uttar Pradesh 1st innings: 206 all out in 84.4 overs (Tanmay Srivastava 67, Prashant Gupta 41, Eklavya Dwivedi 23; Shardul Thakur 6/53).
Mumbai 1st innings: 42 for three in 17 overs (Amit Mishra 2/13).
