Glamorgan 216 for 6 (Cooke 84, Ashraf 3-38) beat Yorkshire 215 for 5 (Hodgson 90) by five wickets
Scorecard
A narrow victory by four wickets with seven balls remaining for Glamorgan at Headingley ensured their passage into the semi-finals as Yorkshire ended a bleak Yorkshire Bank 40 season with their ninth defeat in 12 matches.
Yorkshire won the toss at Headingley and opted to bat but lost Jonathan Tattersall and Alex Lees quickly. But Daniel Hodgson's 90, aided by Kane Williamson and Adam Lyth helped the home side to 215-5 from their 40 overs.
Glamorgan also started with a wobble but Chris Cooke (84) and Jim Allenby (40) got them on track, before Graham Wagg's 31 off 17 balls saw them home.
Captained by Richard Pyrah in the absence of Andrew Gale, who was rested, Yorkshire's young side gave a good account of themselves but Glamorgan's batsmen always had a 216 target well within their sights.
They were in some trouble when openers Gareth Rees and Mark Wallace soon departed to the new-ball pairing of local league journeyman Iain Wardlaw and Moin Ashraf.
But Cooke led the revival with a brisk 84 from 78 balls with six fours and two sixes before he holed out to Oliver Robinson, who took a spectacular catch on the midwicket boundary.
Allenby, Marcus North and Murray Goodwin all made useful contributions but it was the firepower of Wagg that proved decisive in the end. With 31 wanted from four overs he tore into Pyrah, lashing him for three sixes in four balls.
Ashraf claimed him as his third victim - Wagg's 31 including a four and four sixes - but by then Glamorgan were only six short of the finishing line.