Surrey missed out on Pro40 promotion after a seven-wicket hammering by Somerset at Taunton.
They were pipped to third place by Hampshire, who won at Headingley.
The Sabres, with only one previous win, reached a target of 178 with 19.3 overs to spare, thanks to Arul Suppiah (51), James Hildreth (39) and Matt Wood (37).
Earlier the home spinners, led by Wes Durston (3-44) had tied Surrey down, with only Jon Batty (40) and Mark Butcher (38) making much impression.
Surrey's innings was always a struggle after openers Scott Newman and Ali Brown fell with only 30 on the board.
Charl Willoughby (2-26) produced a mean six-over opening spell which cost only 16 runs before the spinners took over.
The highlight of the innings was a stunning one-handed catch by Suppiah at point off Willoughby to dismiss Brown.
It gave Willoughby his 100th wicket in all competitions of an impressive first season with Somerset.
After Suppiah's half century, Ian Blackwell, sidelined for much of Somerset's disappointing season, gave a cameo reminder of his huge ability with 27 not out, including six boundaries.