In reply, Surrey posted 171, Chris Jordan making a career-best 73, from 35 balls, with seven fours and four sixes
Taunton: Somerset 218-8, Surrey 171-9 - Somerset win by 47 runs
Will Smeed fell two short of a first Vitality Blast century as Somerset made sure of a home quarter-final with a 47-run win over South Group winners Surrey at the Cooper Associates County Ground, Taunton.
The 20-year-old opener smashed 10 fours and five sixes in his 51-ball innings, sharing a scintillating third-wicket stand of 165 in 12.3 overs with skipper Tom Abell, who hit 70, to help the hosts reach 218 for 8 after losing the toss.
In reply, Surrey posted 171, Chris Jordan making a career-best 73, from 35 balls, with seven fours and four sixes, only Laurie Evans (39) offering any meaningful support. Craig Overton returned 4 for 25.
The result meant Somerset finished runners-up to their opponents in the group. Abell joined Smeed in the fourth over, which had seen Tom Banton run himself out for nine, attempting a second run, and Rilee Rossouw caught in the deep second ball.
Surrey could feel satisfied at the end of the six-over powerplay, reached with the home side 44 for 2. But the next ten and a half overs saw Smeed and Abell smite 150, clearing the ropes eight times between them. Their partnership also yielded 17 fours.
Smeed brought up a 29-ball fifty in the tenth over and the century stand was completed three overs later from 53 deliveries. Abell lost nothing in comparison with his partner and moved to a half-century off 27 balls in the 14th over, sent down by Cameron Steel, which cost 23.
Somerset looked on course for 250 until Reece Topley returned to have the captain caught at deep backward square, having faced 51 deliveries, and Smeed followed in the same over, miscuing a catch to deep midwicket.
Craig Overton picked up four wickets for Somerset (Harry Trump/Getty Images)
At that point, Somerset were 197 for 4 with three overs to build. But Topley finished with a creditable 2 for 26, while Atkinson and Jordan, who claimed three wickets in the final over, ensured only 21 were added.
Surrey made a disastrous start to their innings, Overton having Will Jacks and Tom Curran caught at mid-on off the second and fourth balls of the opening over. The seamer followed up by having Jamie Smith taken at slip in the third over to leave the visitors 11 for 3.
Evans and Jordan addressed a potentially embarrassing situation with aplomb. When Jordan hit Lewis Gregory for 6,6,4,6 in a ninth over that cost 23, his side were back in the game.
Evans had faced 32 balls, hitting three fours and two sixes, when Roelof van der Merwe had him caught at long-off in the tenth over, which ended with Surrey 94 for 4. Jordan breezed to his maiden Blast fifty off 22 balls, with five fours and two sixes, but it never looked like being enough.
There was a nice sub-plot in the 14th over when Overton bowled to twin brother Jamie, who had struck him with a bouncer and forced him to retire from the County Championship clash between the sides at Taunton this season.
Revenge was sweet when Jamie edged the fifth delivery though to wicketkeeper Tom Banton and Craig celebrated football-style.
When Jordan fell to Peter Siddle in the 17th over, caught at deep extra cover by George Bartlett, substituting for Abell, who had injured himself batting, Surrey's race was run. Atkinson was unable to bat as his side suffered only their third group defeat.