The visitors, set 161 to win, stormed home with 9.3 overs to spare, Penberthy hitting an assured, unbeaten 74.
Loye had batted impressively to reach 68 when he skied a delivery from leg-spinner Amer Khan and was caught at mid-on, with his side only 12 short of victory. He had stroked six fours in his 93-ball innings, and the left-handed Penberthy's unbeaten innings also contained six boundaries, from 84 deliveries.
At Old Trafford Graham Lloyd's rich vein of form for Lancashire continued as he hit 134 to help defeat Durham by 57 runs. Lloyd, who scored a 102 against them in the opening county match of the season, shared a stand of 197 with John Crawley.
Steve Watkin's opening spell of three for seven in six overs set up a win for Glamorgan even though the wet Welsh weather did its best to steal the deserved points away.
The rain that ruined Glamorgan's chances of an opening County Championship victory on Saturday sent them scurrying for their calculators yesterday, before the readjusted-target win was confirmed.
After restricting Warwickshire, who won the toss, to 147 for seven off a full 40 overs, Glamorgan had reached 81 for 3 off 20 overs when the rain returned.
When the calculators were finally packed away, after initial confusion with the new Duckworth-Lewis method of determining rain-interrupted matches, Glamorgan were adjudged winners by "plus 17 runs''.
Watkin sent back Dominic Ostler, Neil Smith and Glamorgan old boy David Hemp, to leave Warwickshire struggling on 28 for 3 by the 12th over.
Dougie Brown and Andy Moles put on 47 for the fourth wicket in 11 overs, before Adrian Dale got rid of both of them in the same over. Watkin returned to complete his allotted eight overs and had Ashley Giles caught by Matthew Maynard, making ground from midwicket to square leg, with his second ball.
Warwickshire's total did not look enough, despite the slowness of the wicket and outfield.
When Hugh Morris lifted Graeme Welch straight back over his head for six, that feeling was confirmed.
Warwickshire will start their Benson and Hedges Cup campaign at Worcestershire amid fears that their new captain, Tim Munton, may need back surgery.
A decision will be made today when the 31-year-old paceman has a second appointment with a specialist in Nottingham.
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