Paul Tosh completed the first-half rout in the 32nd minute, collecting a Thompson cross to score from 20 yards.
Arbroath's Robert Ross headed in late on, but Aaron Sinclair cleared.
Montrose: Bennett, McNalley (Nicky Smith 67), Cambell, Crighton, Pope, Hegarty, Milligan, Davidson, Thompson (McCord 85), Sinclair, Tosh. Subs Not Used: Wood, Collier, Fleming.
Booked: Pope, McNalley, Hegarty.
Goals: Cambell 8, Hegarty 22, Tosh 32.
Arbroath: Hill, McMullan, Malcolm, Griffin, McCulloch (Ross 46), Jordyn Sheerin, Falkingham, Gibson (Shields 66), McGowan, Paul Sheerin (Dimilta 46), Swankie. Subs Not Used: Burns, McIlravey.
Booked: Jordyn Sheerin.
Ref: K Clancy