FL t20 semi-final, Edgbaston
Somerset 94-6 (10ovs) beat Hampshire 138-4 (15.5ovs) (D/L) in a one-over eliminator
Buttler hit three sixes and a four in making 32 off 16 balls
Somerset beat Hampshire in the day's second one-over eliminator to set up an FL t20 final with Leicestershire.
Shahid Afridi hit a Twenty20 career-best 80 as reigning champions Hampshire made 138-4 from an innings reduced to 15.5 overs after three rain delays.
With a revised target of 95 from 10 overs via the Duckworth/Lewis method, Somerset fell one run short of victory.
But their total of 16-0 from the additional six balls proved enough as Hampshire could only post 5-1.
The victory will be seen as retribution by a Somerset side who lost last year's final to Hampshire at the Rose Bowl by virtue of losing more wickets than their opponents after the scores finished tied.
The match was reduced to 16 overs per side following two bouts of rain in Hampshire's opening four overs.
Somerset v Hants T20 history
- Played - 5
- Somerset- 3 wins
- Hampshire - 2 wins
- One abandonment
Dominic Cork's side looked dominant, despite the loss of Jimmy Adams for 18, as Afridi smashed five sixes and six fours on his way to surpassing his highest score of 54 for Pakistan against Sri Lanka at Lord's in 2009, by 26 runs.
Having put on a partnership of 64 off 31 deliveries with Afridi, James Vince was caught by Keiron Pollard off Murali Kartik for 22 before play was again suspended with just one ball of Hampshire's 16 overs remaining.
With Somerset chasing a revised target of 95 from 10 overs, Trescothick and Kieswetter set about their task with vigour, posting a partnership of 40 off the first three overs.
But Kieswetter then went for 14, hitting Danny Briggs' delivery straight to James Vince at long on, as Somerset lost three wickets for just 10 runs.
Vince claimed a second catch when Imran Tahir dismissed Kieron Pollard for eight before Trescothick was sent back to the pavilion for 28 by the South Africa international's next delivery.
But Jos Buttler resumed Somerset's pressure on the Hampshire bowlers, racing to 32 off 15 balls to leave his side needing two to win.
Needing one off the final ball, Hampshire closed in their field and the tactic worked as Arul Suppiah was run out meaning the second semi-final would also be determined by a one-over eliminator.
Kieswetter and Buttler then returned to the field as Somerset posted 16 from their additional six balls.
Alfonso Thomas then frustrated the Hampshire batsmen, with Afridi being caught by Suppiah, as
last year's winners
were left 12 runs short of securing a place in the final.