A tight final over from Jim Allenby earned Glamorgan a two-run victory over Nottinghamshire under the Duckworth-Lewis Method in a rain-affected Clydesdale Bank 40 clash at Swansea.
Defeat meant the Outlaws fail to take the opportunity of going top of Group B, while Glamorgan maintain their slim hopes of qualification for the semi-finals.
Nottinghamshire had reached 77-4 in 18 overs in pursuit of 182 to win when rain interrupted play for more than an hour.
When play restarted the Outlaws were required to reach 110 to win, meaning they needed 33 off the final three overs.
Samit Patel and Chris Read managed 13 from Allenby's first over and six came from the first five balls of Graham Wagg's final over before Patel was caught at long-on off the final delivery.
That left the visitors requiring 13 from Allenby's final over - but Read and Scott Elstone could only manage five from the first five balls to give the Dragons victory, despite Read hitting a six off the final ball.
The Glamorgan spinners, and particularly Cosker, checked the visitors' progress at the start of their reply.
Cosker, who opened the bowling, struck in the third over to have Michael Lumb caught at midwicket, and four overs later Alex Hales was stumped off the 34-year-old's bowling to leave Nottinghamshire 24 for two.
Although Cosker got two crucial wickets he was struck for two sixes off Riki Wessels, who made 38 -
including a third six off Wagg - before being caught at square leg off Robert Croft.
At that stage Notts were two runs ahead of the required rate - but just before they went off for rain Cosker trapped Adam Voges leg before wicket and the rate went up to 87, which meant Glamorgan were winning.
The backbone of Glamorgan's 181 for eight, after they won the toss, was Ben Wright's 62 from 70 balls which included two straight sixes.
With Marcus North he put on 61 in 15 overs after Glamorgan had struggled to 63 for four and then 88 for five.
Glamorgan had got off to a breezy enough start with Gareth Rees and Mark Wallace accruing 38 in the first six overs.
Rees struck two sixes off Samit Patel, who opened the bowling on the slow pitch - the same one which was used for the County Championship Division Two match against Gloucestershire.
But both Rees and Wallace holed out off Andy Carter and Graham White, who ended with three for 28 from his eight overs.
White struck three times in as many overs. He trapped Chris Cooke lbw, while Allenby became the third to hole out.
After Stewart Walters was caught at slip off Patel it was left to North and Wright to pick up the pieces.
In the fourth over before the end North was also caught attempting a big shot, but Wright helped to add 23 from the last over - including a six off Patel.