The Dons, who beat Inverness to win the League Cup in March, scored first in Sunday's Scottish Cup semi-final before his side conceded twice to St Johnstone's Stevie May in the second half.
Former Celtic striker McGinn believes Aberdeen had the better of the chances at Ibrox but admitted the Granite City club were not good enough in attack to place more pressure on the eventually victorious Saints.
"On the day we had the better chances and St Johnstone just had two - but they scored both," said McGinn who featured when the Dons hammered St Johnstone 4-0 in the League Cup semi-final in February.
"We are pleased with the performance but know we should have been more clinical. The League Cup semi-final was not a 4-0 game but we took our chances. This time Saints took theirs."
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