The hosts had posted 356 in their first innings and are still 76 runs ahead and well on course to take the crucial first innings lead.
For defending champions Vidarbha, who resumed at their overnight score of 63 for 2, veteran Wasim Jaffer stood out with his 98-run knock.
Jaffer in his 225-ball stay at the crease, stuck eight fours and a six.
But Saurashtra hit at right intervals as they roared back into the game, which was drifting away due to Jaffer's knock.
After Jaffer departed, Vidarbha's lower middle order batsman Mohit Kale (66) played a crucial knock.
Even Akshay Wakhare (22) and Suniket Bingewar (30) got starts but they failed to convert.
Vidarbha's no 10 Aditya Thakare (3) and no 11 Yash Thakur (0) were holding fort at stumps.
The win meant that the multiple Ranji champions avoided relegation to a lower Group.
Chasing the 91-run target, Mumbai resumed from their overnight score of 77 for no loss and hit off the required 14 runs in the morning. But they lost their opener Vikrant Auti (34) when the team score was 79.
The other opener Jay Bista (49 not out) then completed the proceedings in 24.2 overs along with Yashasvi Jaiswal (0 not out) at the other end.
The hosts then bundled out the opposition for 149 in the second innings to lay the foundation of the consolation win.
Pacer Tushar Deshpande, who ended the game with nine wickets, was adjudged as the Man of the Match.
Mumbai 6 points, Chattisgarh 0 points.
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