Lancashire overhauled Gloucestershire's target of 185 in the last over of their match at Old Trafford to go top of Group A in the CB40.
On a wicket that was not conducive to free-flowing batting, man-of-the-match Karl Brown (60) and Paul Horton (46) put on a vital 82 for the fourth wicket after Stephen Moore set the foundations for the chase with a bright 37.
David Payne took 3-39 in his eight overs to keep Gloucestershire in the hunt, but small late contributions from Gareth Cross (seven not out from five balls) and Ajmal Shahzad (10 from five) ensured Lancashire came away with the two points.
Gloucestershire had looked to be heading for a score in the 160s until a late assault on Stephen Parry's left arm spin by Ian Cockbain (58), who hit three of the final four deliveries of the innings for six.
Parry (1-48) and been economical until that last over, as was fellow slow-left-armer Gary Keedy (1-27) as the pitch took plenty of low turn, while Shahzad (2-34) and Oliver Newby (2-24) both picked up important wickets.
Hamish Marshall had made 23 when he was trapped lbw by a Newby yorker as the Gladiators struggled to 35-3.
Alex Gidman and Dan Housego steadied the ship with a 47-run partnership before Newby returned to demolish Gidman's stumps and Keedy then bowled Housego for a gritty 43.
In the reply, Moore and Ashwell Prince gave Lancashire a solid start to their reply, putting on 43 before South African Prince was surprised by extra bounce from Payne.
But Horton and Brown overcame the tough batting conditions to set up the win before Horton was trapped lbw to James Fuller and Brown holed out to Payne.
Victory puts Lancashire top of Group A