Batting first, Tamil Nadu scored 151 for eight with Abhinav Mukund top-scoring with 41. Seamer Alok Pratap Singh took 3/15 while Mohammed Shami scalped 2/30.
The India international now has five wickets from two games.
Shami will join the Indian ODI squad in Mumbai tomorrow as they prepare to leave on January 5.
In reply, Bengal were skittled out for 82 in 15.5 overs with Rahil grabbing 5/12.
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Only Shreevats Goswami (31) and Sudip Chatterjee (18) added 49 runs for the third wicket before Bengal lost their last eight wickets for only 24 runs.
Tamil Nadu now has won both their matches and have eight points while Bengal remain on 4 points from two games.
Brief Scores: Tamil Nadu 151/8 in 20 overs (Abhinav Mukund 41, Anthony Dhas 28, Alok Pratap Singh 3/15, Mohd Shami 2/30)
Bengal 82 all out in 15.5 overs (Shreevats Goswami 31, Rahil Shah 5/12). TN won by 69 runs.