On a scorching day at Taunton, Hampshire openers Maia Bouchier and Charli Knott put on 80 before Chloe Skelton took a fine catch over her shoulder at mid-on to send Bouchier on her way for 43 from 26 balls with eight boundaries.
In her final game before returning to Australia, Knott holed out to international team-mate Wellington at long-on 10 balls later for 43 from 34 balls.
Georgia Adams (10) and Rhianna Southby fell in successive deliveries to Charlie Dean (3-25), while Abi Norgrove was run out in the next over.
But Kemp went through the gears, with seven fours and two sixes in her 38-ball stay which guided the visitors to 169-6.
Seeking their first win in their seventh match, Somerset fell to 19-2 after four overs but Holland shared a stand of 52 with Sophie Luff (23) and then 63 with Wellington on her way to a career-best T20 innings of 60 from 53 balls, to set up a tense finale.
Wellington hit 44 from 25 balls but fell in the final over as the hosts came up just short at 164-6.
