Williamson played in two Scottish League Cup Finals, winning the trophy once.
[1][2] In 1975 he scored a hat-trick for Aberdeen in a 3–2 win against Celtic when playing at the time in midfield.
[3] He became only the second player at the time to score three or more goals in a single game playing for Aberdeen against Celtic, following in the footsteps of George Hamilton.
[1][4] Williamson picked up a winners medal from the 1976 Scottish League Cup Final 2–1 victory against Celtic.
His stay at Tannadice was short with his league appearances adding up to only 11 games in which he scored once.