The match score was reduced to one hole when Ferguson took the tenth with a bogey five, but Milligan restored his two hole lead by winning the eleventh, though a par was good enough to win the hole on this occasion, following his hole in one there in the previous round.
A par five at the twelfth was enough to put Milligan three up with six to play but a run of three holes from the thirteenth which included a bogey and two double bogeys from Milligan saw Ferguson take full advantage and square the match after seventeen.
The players halved the final hole in fours and the tie progressed into extra holes. As at the start of the tie, the first hole of the extra holes was halved in par fours but on this occasion the roles were reversed at the second, with Ferguson securing a winning par three to Milligan's bogey four, to progress to the final for the third successive year.
Addie opened his semi final by winning the first with a birdie three, only to see McDonald square the match with a birdie two at the second.
A second successive birdie was enough to give McDonald the lead after three holes and he extended his advantage to three hoples after five played, with a par four at the fourth and a winning bogey four at the fifth after Addie struggled to a double bogey five.
Addie hit back at the sixth, winning with a par four to reduce the deficit to two holes and when McDonald struggled at the ninth, Addie further reduced the deficit to one hole at the turn.
At the par five twelfth, Addie birdied the hole to square the match overall and the match remained level through fourteen before McDonald again went ahead after Addie couldn't match his bogey five there.
Par fours at both the sixteenth and seventeenth were sufficient for Addie to take both holes and turn one hole deficit into a single hole lead with just the final hole to play.
At the eighteenth, a short par four, McDonald closed with a birdie three but Addie held his nerve to match McDonald's three and take the tie, and the place in the final with a one hole victory.
The final tees off at Prestwick Golf Club on Thursday evening, 9th August, at 4.30 p.m.