Dawid Malan's unbeaten 113, backed up by an impressive bowling display, earned Middlesex a 19-run Duckworth-Lewis win against Gloucestershire at Lord's which keeps alive their hopes of qualifying for the Yorkshire Bank 40 semi-finals.
Gloucestershire's own chances of making it out of Group C received a heavy blow as they could make only 186-9 in reply to Middlesex's 206-5.
A short shower, which interrupted the early part of the Middlesex innings, led to the match becoming a 38-over per side affair, with Gloucestershire's target being adjusted to 206 under the Duckworth-Lewis calculations.
Malan underpinned the Middlesex batting effort with his first hundred of a prolific YB40 season, facing 116 balls and hitting two sixes and nine fours in taking his run tally for the competition to 552 at an average of 78.85.
Eoin Morgan, unusually becalmed as he laboured through 48 balls, was Middlesex's next best scorer with 22 and at the halfway stage it seemed as if Gloucestershire, joint top of Group C when the match began with 13 points from their previous nine games, were well in contention.
Steven Finn, given fresh hope of an England Test return next week by news of Tim Bresnan's stress fracture injury, had Hamish Marshall caught at point from the first ball of Gloucestershire's run chase, and then James Harris pulled off a smart return catch to remove Chris Dent for two.
Much depended on Gloucestershire captain Michael Klinger, whose 46 took his own YB40 run tally to 575 at 95.83, and for a while he was well supported by Ian Cockbain in a stand of 81 for the third wicket.
But Cockbain then skied to mid-off, charging at Gareth Berg's medium pace, and Klinger - who had also been dropped on 13 and 19 - was stumped as he went down the pitch to try to heave a ball from left-arm spinner Ravi Patel into the Grandstand.
Patel then had Alex Gidman leg before wicket for 19 and Harris returned to bowl James Fuller for just one. Benny Howell straight drove Toby Roland-Jones for six and swung him for another maximum next ball, but on 39 his bright effort ended with a skied catch to extra cover off the impressive Harris, who finished with 3-30.
There were also two wickets for Roland-Jones as Gloucestershire's late order swung with increasing desperation, with Gareth Roderick going for 13 and Ed Young for 12.
Malan was the only Middlesex batsman to get on top of some disciplined but largely unthreatening Gloucestershire bowling, with slow left-armer Young perhaps the pick of the attack with some clever variations of pace.
Paul Stirling fell to the first ball of the second over, inside-edging a drive into his stumps against Craig Miles, but Malan added 51 in just under 10 overs with Joe Denly for the second wicket before Denly was caught at extra cover for 21 from a leading edge as he looked to force medium-pacer Howell straight.
Morgan looked completely out of touch on a two-paced pitch, struggling through 45 balls for a mere 15 runs before lofting Miles over long-on for six for what proved to be his only boundary.
On 22, and having been very much the junior partner in a stand of 65 with Malan, he tried a big hit at Chris Dent's occasional left-arm spin and skied to Klinger to end a curiously subdued innings from one of cricket's most destructive one-day batsmen.
Neil Dexter did manage to increase the scoring rate with 20 from 21 balls, helping Malan to put on a further 58 in eight overs for the fourth wicket, but he then mis-hit to point trying to slash away a ball from left-arm seamer David Payne.
Gareth Berg fell cheaply, bowled for three by Fuller, but Malan celebrated reaching his first YB40 century of the season by swinging Payne for six over the long deep midwicket boundary and, in the final over of the innings from Fuller, he added a second six to the same area. With John Simpson also taking a four from Fuller's last over, Middlesex's total was pushed above 200.