Glamorgan 204 for 7 beat Somerset 201 for 8 by three wickets
A weakened Somerset side suffered their first Clydesdale Bank 40 defeat of the season as they went down by three wickets to Glamorgan Dragons at the Swalec Stadium.
Quick bowler Will Owen recorded figures of 4 for 31 in restricting Somerset, who were without skipper Marcus Trescothick (ankle) and Murali Kartik (back), to 201 for 8 in their 40 overs.
And in reply, helped by a career-best 43 from Nick James, and contributions down the order from Michael O'Shea and Chris Cooke, Glamorgan reached their target with nine balls to spare to celebrate their third victory of the campaign.
Despite the reversal Somerset still head Group C and remain well-placed to reach the semi-finals. Acting captain Alfonso Thomas won the toss and opted to bat, but his decision was called into question when Owen struck twice.
First he removed Craig Kieswetter for a duck with the fourth ball of the match and two overs later he produced a great delivery to bowl Nick Compton, who also failed to score. It left Somerset on 6 for 2.
James Hildreth and Peter Trego did their best to repair the damage putting on 60 in 12 overs for the third wicket. But offspinner O'Shea broke the partnership in his opening over to have Hildreth caught by Dean Cosker brilliantly at short midwicket.
O'Shea struck again having Jos Buttler caught by Wallace from an attempted slog sweep. O'Shea was struck for a big six off Trego but still recorded decent figures 8-0-32-2.
Trego had reached his 50 from 74 balls before he was caught behind to give a third wicket to Owen who claimed a fourth in his next over when he knocked Craig Meschede's off stump over as Somerset were reduced to 145 for 6 in the 32nd over. But cameos from Arul Suppiah and Thomas, who were both caught in pursuit of late runs, guided Somerset towards a competitive total.
Glamorgan brought up their 50 in the seventh over and the openers, Alviro Petersen and Matthew Rees, added 69 in 10.2 overs to give Glamorgan a useful platform. However, both batsmen were out within the space of three overs as the home side found themselves 81 for 2, before that became 99 for 3 when Jim Allenby holed out unnecessarily.
Glamorgan reached the halfway point of their chase in the 19th over but kept losing wickets at regular intervals including that of James who was well caught at mid-on by Suppiah off George Dockrell after putting on 58 with Stewart Walters for the fourth wicket.
Another great catch at short mid-wicket by Hildreth saw the end of Wallace as Glamorgan slumped to 171 for 7 but O'Shea and Cooke held their nerve to knock off the arrears