Chasing 152, Karnataka rode on a quickfire 51 (33 balls; 5x4, 2x6) from Lokesh Rahul to chase down the target in 19.2 overs.
India discard Robin Uthappa (41 from 35b; 5x4, 1x6) helped Karnataka recover from a jittery start when they were 37/2. Later Rahul put on a 49-run fourth wicket partnership with Manish Pandey (20) to build the foundation before Stuart Binny steered the side home with an unbeaten 21 (18b; 1x4, 1x6).
Earlier, Bengal had a typical middle-order collapse after skipper Laxmi Ratan Shukla opted to bat as they were reduced to 74 for five with Sayan Sekhar Mondal only shining at the top of the order with an useful 42 (30b;5x4, 1x6).
The duo of Arnab Nandi (37 not out, 17b; 3x4, 3x6) and Debabrata Das (31, 24b; 2x4, 1x6) repaired the damage taking the side to a respectable total. Bengal finished with eight points from 4 matches as they made an early exit along with defending champions Baroda (4/3) from group B.
Karnataka, Uttar Pradesh and Punjab -- all with 12 points each from three matches each -- remain in the three-way race for the two berths for the last four.
Bengal 151/7; 20 overs (Sayan Sekhar Mondal 42, Arnab Nandi 37 not out, Debabrata Das 31; R Vinay Kumar 2/30, S L Akshay 2/24, Krishnappa Gowtham 2/26). Karnataka 152/6; 19.2 overs (Lokesh Rahul 51, Robin Uthappa 41; Shami Ahmed 3/39, Mondal 2/26). Karnataka won by 4 wickets.