Replying to Railways' paltry first innings total of 217, Mumbai ended day two of the four-day tie at 330 for 9 for a lead of 113 on a Wankhede Stadium track offering appreciable turn to the slow bowlers, indicated by the 28-year-old Sharma's impressive figures of 6 for 90.
At stumps, Nikhil Patil was unbeaten with a well-made 82 along with number 11 batsman Vishal Dabholkar (0) after left-handed Herwadkar had played the sheet-anchor's role with aplomb in his 277-minute stay in which he hit 15 fours and 2 sixes.
Sharma then produced a magical spell to dismiss Iyer, Mumbai captain Aditya Tare and Siddhesh Lad while off-spinner Arnab Nandi accounted for Suryakumar Yadav to leave the home team gasping at 147 for 6.
UP-born Sharma, who played in the Adelaide Test against Australia during India's tour last season, had the aggressive Iyer caught behind off a forcing shot and then bamboozled Tare for a duck and Lad for 5.
Also Read
Herwadkar found in Patil the ideal man to counter the spin threat. The latter used his feet convincingly, either to go forward or play back, and the duo put on a seventh wicket partnership of 124 at run-a-minute to regain the initiative.
Herwadkar was out just before tea, falling to Sharma's guiles, but Patil -- who hit four sixes over the straight field and two fours -- batted with the tail to prolong the innings.
Brief Scores: