A blistering innings of 79 from Peter Trego and some canny bowling by Alfonso Thomas gave Somerset their first Twenty20 Cup success this season at the fourth attempt as they defeated Glamorgan by 15 runs.
The Sabres posted 185 for six after losing the toss, with Trego hitting seven fours and three sixes in his 50-ball innings. David Harrison was the pick of the Dragons bowlers with two for 32.
In reply, Glamorgan were restricted to 170 for five, despite 76 not out off 51 balls from Herschelle Gibbs. Thomas took one for 21 from his four overs, varying his pace and line cleverly in the closing stages of this Mid/West/Wales Division clash.
Arul Suppiah also made an important contribution, conceding 27 from four overs of left-arm spin, to help Thomas push up the required run-rate after Glamorgan looked to be on top.
Gibbs hit nine fours and two sixes in a brilliant exhibition, while Robert Croft also played well for his 50 off 37 balls. The pair took the score to 117 for one in the 13th over before Thomas had Croft caught at backward point with a slower ball.
Glamorgan gradually lost their way in failing light, and after Thomas had run out Mike Powell, Mark Turner picked up two wickets in the final over to seal the visitors' fate.
Earlier, Somerset lost Marcus Trescothick to the second ball of the match and the first he received. The former England opener was caught behind swinging at a good length ball from Harrison.
It was 27 for two when Justin Langer skied a catch to Jamie Dalrymple at mid-wicket, but already Trego was timing the ball superbly and Ian Blackwell helped take the score to 65 before departing disappointingly for 14 to an attempted reverse sweep off Dean Cosker.
Kieswetter should have been run out for four, but Robert Croft failed to gather a low return from Gibbs at the bowler's end and it proved a costly error.
The wicketkeeper went on to help Trego add 59, scoring his runs off 26 balls, with three fours and two sixes, the latter coming off successive balls from Ryan Watkins in the 17th over.
Trego continued to play powerfully on both sides of the wicket until his departure at 124 for four. Even a brief interruption by a male streaker failed to disrupt his concentration.
After Kieswetter followed, Ben Phillips smashed 17 off just seven balls and Suppiah hit the last ball of the innings for six to ensure a very competitive total.