Hampshire 164 for 6 (McDermott 47, Hollman 2-12) beat Middlesex 159 for 7 (Holden 53, Higgins 43, Turner 3-30) by five runs
The 22-year-old captured the wicket of Middlesex captain Stephen Eskinazi with his first ball in the tournament, finishing with 3 for 30 as the Hawks successfully defended a modest total of 164 for 6.
But Hampshire's death bowlers held their nerve to ensure the home side remain winless in the competition, equalling their longest losing start to a campaign of seven defeats in 2006 and 2009.
Hampshire skipper James Vince, who had smashed a match-winning 88 not out in the sides' first meeting of the tournament, missed out this time after driving Josh de Caires' second ball tamely to mid-off.
That move paid off as the quick hrashed 31 from 21 and he and Ross Whiteley, with an unbeaten 28 from 20, hauled Hampshire above 150 but Higgins, with four consecutive dot balls in the penultimate over, ensured they fell short of par.
However, their total looked more than substantial after two overs of the Middlesex reply, with just two extras on the board and both openers back in the pavilion with ducks against their name.
Eskinazi was caught miscuing a pull to midwicket off Turner's first delivery and Joe Cracknell followed five balls later, leg before - but Holden and Pieter Malan kick-started the innings with a stand of 43 from 23.
Malan, having advanced to 18 with two powerful leg-side blows off Wood, attempted to do the same against Nathan Ellis just before the end of the powerplay and was caught in the deep.
Holden displayed a knack of picking out the gaps, carving Scott Currie to the cover boundary and clipping his next ball to leg for four more as Middlesex kept pace with the required run-rate.
The left-hander brought up his 50 from 26 balls and Higgins was a more than capable foil in their partnership, bisecting the leg-side fielders perfectly to register successive fours off Wood.
But Liam Dawson tilted the contest back in Hampshire's favour, tempting Holden to top-edge a pull to short fine leg and Turner claimed his third wicket before Vince raced from mid-off and dived to pouch a skier from Higgins.
Despite two boundaries by Martin Andersson to keep Middlesex in contention, a target of 15 from the final over proved too steep.