At close of play on the second day, Mumbai had reached 302 for seven in reply to Karnataka's first innings score of 195 with Ajit Agarkar on 20 and Vinayak Samant on 13 at the crease.
Resuming this morning, Karnataka lost their last wicket of B Akhil in the third over of the day, adding just six runs to their overnight score of 189 for nine to be bowled out for 195.
Wasim Jaffer and Sahil Kukreja, opening the innings for the defending champions, gave Mumbai a solid start both putting on 118 for the first wicket.
Both the openers played sensible cricket with neither pace nor spin affecting them.
It was Kukreja who got going first, essaying a beautiful on-drive off Kumble. In fact, both these batsmen handled the star leg spinner superbly, negating him in the process and putting Mumbai on a solid foundation.
Kukreja, then, took a liking for medium pacer B Akhil hitting the bowler for three boundaries in one over all-round the wicket with an off drive, an on-drive and an elegant pull to the fence.
Jaffer at the other end took on Kumble with a superb cover-drive and then cut the other spinner, left-armer Sunil Joshi to the point boundary.
The India Test opener then brought up his 50 with an on-driven four off Vinay Kumar. Jaffer's 50 came off 93 balls with eight boundaries.
Kukreja also brought up his 50 soon after. His 50 coming in a stay of 81 balls and was inclusive of nine boundaries to take Mumbai to lunch at 110 for no loss.
Karnataka, however, struck back after lunch as the proceedings took a dramatic turnaround early in the second session as N C Aiyappa opened the floodgates. He got the first breakthrough getting Wasim Jaffer clean bowled as the batsman, late in leaning forward, played on to an in-cutter for 55 to leave Mumbai on 118 for one.
Soon it was 121 for two with Sunil Joshi getting youngster Ajinkya Rahane (0) out leg-before as the batsman padded up without offering a shot.
In the next over, Aiyappa got the other important breakthrough of Sahil Kukreja as he lunged at a full delivery that shaped away for wicketkeeper T ilak Naidu to complete the catch. Kukreja made 66 and Mumbai had lost three wickets in nine balls to be in some sort of trouble at 125 for three.
Prashant Naik then joined his captain Amol Muzumdar and showed a mature head on young shoulders, playing the bowling on merit and eschewing all risks as he and his captain put on 48 runs for the fourth wicket before Muzumdar was trapped in front with a faster delivery from Anil Kumble for 23 with Mumbai on 173 for four.
Naik grew in confidence as he drove Kumble and Vinay Kumar through covers before square driving B Akhil.
Abhishek Nayar, the next man in, counter-attacked with a hat-trick of boundaries off Kumble. He chipped the first over midwicket, lofted the next to the sqaure-leg boundary before cutting the last through cover. In Kumble's next over, he punched one through covers as Mumbai took the lead. Nayar, who crouches in his stance before shuffling across from his outside-leg guard, then turned his attention to Akhil, driving him to the straight boundary.
Naik too caught the attacking virus and stepped down the track to loft C Raghu to the long-on boundary for the first six of the game.
Then, in the last over before tea, after he had featured in a 44-run partnership in 39 balls, Nayar paid for his impetuosity - missing a reverse-sweep off Joshi to be adjudged lbw.
Ramesh Powar also did not last long, holding out to C Raghu at mid-wicket after hitting a six and four off the bowling of Sunil Joshi to leave Mumbai at 231 for six.
Naik then received good support from Ajit Agarkar as he reached his 50 in his debut match off 99 balls with six boundaries and a six.
However, after the two had put on 43 runs, Agarkar called Naik for a non existant run on the off side for the latter to be run out at the striker's end by a direct throw by Vinay Kumar from the covers.
Naik made 78 after facing 152 balls and hit nine boundaries and a six.
Agarkar and Vinayak Samant then added an unbeaten 28 runs for the eighth wicket to take Mumbai's lead past the 100 mark.
Brief Scores (D-2):
Karnataka Ist innings 195 all out Vs Mumbai Ist innings 302 for 7 (Prashant Naik 78, Sahil Kukreja 66, Jaffer 55, Abhishek Nayar 24; Joshi 3 for 67, Aiyappa 2 for 43, Kumble 1 for 85).