Haryana invited Jharkhand to bat first and restricted them to 146 for nine.
While chasing, Guntashveer smashed an unbeaten 65 as Haryana achieved the target losing four wickets, with two overs to spare.
Earlier, Ishank Jaggi 57 off 38 balls studded with three fours and three sixes helped Jharkhand to post good 146.
However, batsmen Ishan Kishan (15) and Shiv Gautam (16) failed to capitalise after starting off well.
Akshadeep Hooda gave initial breakthrough removing Kishan and then Kuldeep Hooda ran through the Jharkhand's innings, picking up five wickets conceding 31 runs.
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For jharkhand, Vikas Singh and Sarfraz Ashraf took a wicket each.
Brief scores: Jharkhand--146 for 9 (Ishank Jaggi 57, Kuldeep Hooda 5-31).
Haryana--149 for 4 off 18 overs (Guntshveer Singh not out 65, Avi Barot 37, Sarfraz Ashraf 1-13).