Glamorgan boosted their hopes of making the Yorkshire Bank 40 semi-finals - and put a dent in Middlesex's in the process - with a 12-run win on the Duckworth/Lewis method in Cardiff.
The Welsh county moved level with Somerset and Gloucestershire at the top of Group C as they successfully defended a total of 153-9 in a contest reduced to 25 overs per side following afternoon rain.
Middlesex's reply started badly when they lost the in-form Dawid Malan for a third-ball duck, knocked over by a superb delivery from Jim Allenby, as they quickly slumped to 32-5.
Simon Jones rolled back the years with two key wickets in as many balls, firstly getting England Lions captain Eoin Morgan caught at deep point by Chris Cooke for nine before then trapping Australian Adam Voges (1) leg before.
Neil Dexter and John Simpson (32) gave Middlesex hope with a sixth-wicket stand of 59, only for the latter to become one of three late victims for experienced left-arm spinner Dean Cosker (3-32).
Dexter bravely kept on swinging until the end, posting the only half-century of the match thanks to five boundaries, before holing out to long-off with 19 needed off the final five balls.
Glamorgan had earlier been indebted to the late momentum provided by Ben Wright, who made 26 off 20 deliveries, and Graham Wagg (20 not out) having at one stage found themselves six down with only 89 on the scoreboard.
Gareth Rees top scored with 32, though the opener took up 53 balls to make his runs. He was eventually dismissed by former team-mate James Harris.
Toby Roland-Jones was the pick of the Middlesex attack, home captain Marcus North one of his victims as the seamer claimed fine figures of 3-13 from his five overs.
Spinner Paul Stirling weighed in with 2-18 and there was also a pair of scalps for Steve Finn, though the England paceman saw 10 runs come from his final over as the Dragons roared late on.