Millbrook came from a goal behind to win 2-1 over Launceston at Jenkins Park and reach the quarter-finals of the Cornwall Senior Cup.
Launceston took the lead on the half-hour mark against their one-league-higher opponents.
But Brook equalised 10 minutes later when skipper Jack Wood finished off after a free-kick.
It took until 10 minutes from time for Millbrook to get the winner, when Sean Thomson slotted home after being left one-on-one with the goalkeeper.