Put into bat, Pujara smashed his way to 138 off 129 balls with 14 boundaries and two sixes as Saurashtra scored a healthy 279 for five in 50 overs.
In reply, 36-year-old Wasim Jaffer smashed 83 off 67 balls with six boundaries and three sixes while Shreyash Iyer scored 59 off 67 balls as Mumbai reached the target with two balls to spare.
In the lower-order wicketkeeper-batsman Sufiyan Sheikh (31) also made useful contribution adding 43 runs for the sixth wicket with T20 specialist Suryakumar Yadav (26).
It was Wilkin Mota (10), who hit two boundaries in the final over bowled by former UP pacer Sudeep Tyagi to end the match with a florish.
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Brief Scores: Saurashtra 279/5 (Cheteshwar Pujara 138, Iqbal Abdullah 2/40).
Mumbai 280/8 in 49.4 overs (Wasim Jaffer 83, Shreyash Iyer 59, Sidharth Trivedi 4/42). Mumbai won by 2 wickets.
Points: Mumbai 4 Saurashtra 0.