Jordan Young almost gave the Gulls a sixth-minute lead when his free-kick went just wide.
The Gulls continued to pile on the early pressure – Sonny-Blu Lo-Everton forced an excellent save from Harrison Foulkes, Sam Dreyer hit the bar from the resulting corner and Jordan Dyer had a 21st-minute goal disallowed for offside.
But seconds later later Deon Moore broke the deadlock as the Torquay striker fired home a Lo-Everton pass.
Ten minutes later Torquay top scorer Young doubled the lead for his 17th goal of the season as he reacted quickest after Dylan Morgan had seen his chance blocked after rounding the goalkeeper.
Dorking – who beat Maidenhead United 2-0 on Wednesday night to reach the semi-final – struggled to impose themselves on the game as Jordan Young headed wide seven minutes into the second half.
Seven minutes later the tie was over as Morgan fired against the Dorking post and Moore – a free-agent signing in March – reacted quickest to make it 3-0.
Charlie Carter forced a good save from Torquay’s Seb Stacey five minutes later with a rare Dorking attack.
Lo-Everton fired an effort wide with 14 minutes to go as Torquay’s confidence flowed before Young got a fourth goal a minute later – Lo-Everton superbly passed to the striker, who beat his marker before firing home.
But Dorking did not give up – Paul McCallum had a header well-saved with eight minutes left and from the resulting corner George Knight headed in a consolation goal.
And the visitors’ endeavours were further rewarded when they got a second in the 89th minute as Alfie Rutherford’s defected effort wrong-footed Stacey.