Clydesdale's Ian Stanger engineered victory with an unbeaten 31 after the earlier batsmen had made a modest winning target of 165 look difficult.
Scotland bowler James Brinkley pulled up with a hamstring strain in his fourth over as Wales batted first. He later had to bat with a runner and is doubtful for tomorrow's game with the ECB England XI.
Spinner Keith Sheridan turned the screw in a niggardly spell of 10 overs which yielded only 15 runs before Kristian Bell took the attack to the bowlers with a splendid 66 as Wales reached 164 for nine in their 50 overs.
Scotland lost Bruce Patterson with just two on the board and although Mike Smith and emergency opener Alec Davies got their heads down they could not force the pace. Davies was bowled by off-spinner Gareth Edwards and George Salmond pulled a long-hop to midwicket.
Drew Parsons and Smith had added a further 27 before the left-hander was bowled through the gate by a Bell leg spinner and almost immediately Smith gave Edwards an easy return catch having compiled 41.
After Sheridan had holed out at cover, it was left to Stanger and Brinkley to steer the Scots home.
Ireland's victory over England in the other game owed much to the economy of spinners McCallan and Dwyer. Replying to Ireland's 171 for nine, England failed by five runs to reach their target.