Saha was more aggressive among the duo hitting seven boundaries and one six en route to 37-ball 54 in a 103-run partnership with Tiwary to set up the chase with 11 balls to spare as Bengal stepped closer to the main round with two wins from as many matches.
The wicketkeeper-batsman was unfortunate to be run-out returning a call for a non-existent single from Tiwary.
Bengal never faced any difficulty chasing the challenging 153, after Saha and rookie Vivek Singh gave an aggressive start.
Singh struck three boundaries in his run-a-ball 14 before being dismissed by Rahul Shukla but Saha kept his onslaught and found a fine ally in Tiwary to unsettle the Jharkhand attack.
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Earlier, Bengal rode on some tidy bowling by rookie offspinner Aamir Gani (2/15) to pull things back after Jharkhand went off to a flier, courtesy Ishank Jaggi and Ishan Kishan's 46-run opening stand that came off 33 balls.
But Jharkhand were let off by some indisciplined show from Bengal fielders who dropped three catches, including two off Kumar Deobrat whose 24-run cameo, from 16 balls with two sixes and one four, pushed their total to 152/9.
Brief Scores
Jharkhand 152/9; 20 overs (Ishank Jaggi 33, Kumar Deobrat 24; Aamir Gani 2/15, Ashok Dinda 2/31, Saurashish Lahiri 2/40) lost to Bengal 153/2; 18.1 overs (Manoj Tiwary 67 not out, Wriddhiman Saha 54) by eight wickets.