Surrey have now gone five NatWest T20 Blast matches without a win after losing to Somerset by four wickets at Taunton.
Gareth Batty's side, who suffered back-to-back defeats to Sussex and Glamorgan after two wash-outs at Hampshire and Glamorgan, saw Somerset top their total of 157-6 with 10 balls remaining.
Former Surrey man Steven Davies was bowled by Jade Dernbach (3-29) for a first-ball duck, two days after he was out for nought in Somerset's loss at Gloucestershire.
The hosts then wilted to 47-5 before Roelof van der Merwe - who muscled Surrey for an unbeaten 165 from 122 balls in the Royal London One-Day Cup earlier this term - and James Hildreth clubbed 69 for the sixth wicket.
Van der Merwe was eventually bowled by Dernbach in the 14th over, for a 19-ball 36, but Craig Overton (35no off 19) picked up the big-hitting mantle, while Hildreth breezed to an unbeaten 45.
Earlier, Aaron Finch hammered 26 from 16 balls up top for Surrey but Ollie Pope was their side's top scorer, striking 46 from 31 balls while putting on 56 with Moises Henriques (26).
Rikki Clarke (16no off 11) and Tom Curran (15no off 9) bumped up the visitors' score late on, Curran thrashing Lewis Gregory over long-on for the only six of the innings.
Somerset and Surrey will meet again on Monday at the same venue as their Specsavers County Championship game commences - Somerset sit seventh in that competition, 30 points behind sixth-placed Surrey.
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