Denny Johnstone scored his ninth goal of the season in all competitions as Morton beat Albion 2-0 in the third round of the William Hill Scottish Cup.Albion started brightly and had a good opportunity to take the lead in the 20th minute when Alistair Love let fly from the middle of the box, but Morton goalkeeper Grant Adam was on hand to keep him at bay.It was the Ladbrokes Championship side who broke the deadlock four minutes before the break when Johnstone latched onto Bobby Barr's low cross before slotting in from close range.Johnstone could have doubled the visitors' lead in the dying embers of the first half but Albion goalkeeper Ross Stewart got down well to keep him out.Morton made it 2-0 in the 88th minute when Joe McKee's effort was deflected into the back of Stewart's net.