This was Mumbai's second successive win after they had beaten Delhi in the lung-opener.
But it was Iyer, who anchored the Mumbai chase and saw them home in 47.2 overs.
Maharashtra skipper Ruturaj Gaikwad (19) could not convert his start and was trapped in front of the wicket by Kulkarni.
Kulkarni then wreaked havoc as he dismissed Naushad Shaikh (0), experienced Kedar Jadhav (5) and Ankit Bawane (0) in quick succession as Maharashtra was reeling at 38/4 in 8.5 overs.
However, Nahar and number six batsman Kazi had other plans and they not only pulled the team out of the trouble but took them to a decent position with their 214 run-stand for the fifth wicket.
Nahar struck seven fours and sixes maximums in his 133 balls knock, while Kazi played the perfect second fiddle, as the duo took on the Mumbai bowlers led by India speedster Shardul Thakur (1/57), who played the game after being released from India squad.
Kazi hammered 12 boundaries and two sixes in his 118-balls innings.
When Nahar was run out by Shams Mulani, Maharashtra was poised at 6/264 and then were able to add only 15 runs.
Chasing 280, Mumbai openers Yashasvi Jaiswal (40) and Prithvi Shaw (34) conjured 67 for the first wicket.
Iyer, who walked in at three, was in his elements and hammered nine boundaries and one six, in his uneaten knock and after Jaiswal perished, he found able partners in Suryakumar Yadav (29), Shivam Dube (47) as they played their roles to perfection.
Dube took the game away from Maharashtra, with his hitting, smashing five fours and a six, and took Mumbai on the cusp of a win. The formalities were completed by Iyer alongside Sarfaraz Khan (15 not out).
Brief Scores: Maharashtra 279/9 (Yash Nahar 119, Azim Kazi 104; Dhawal Kulkarni 5/44, Shardul Thakur 1/57) lost to Mumbai 280/4 (Shreyas Iyer 103 not out, Shivam Dube 47; Satyajeet Bachhav 3/59) by six wickets.
Delhi 354/4 (Nitish Rana 137, Dhruv Shorey 132; Sagar Trivedi 2/66) beat Pondicherry 175 (S Suresh Kumar 42; Kulwant Khejroliya 4/32, Pradeep Sangwan 2/27) by 179 runs.
Rajasthan 199 (Mahipal Lomror 67, Arjit Gupta 45; Rishi Dhawan 6/27, Vaibhav Arora 1/24) lost to Himachal Pradesh 201/6 (Rishi Dhawan 73 not out, Prashant Chopra 39; A Singh 2/46, Ravi Bishnoi 2/60) by four wickets.
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