Number eight Nick Easter ran in two tries as Harlequins beat Nottingham 24-10 to secure a place in the Powergen National Trophy final against Bedford.
Centre Gavin Duffy bagged the other try for the visitors, with fly-half Adrian Jarvis converting all three touchdowns and adding a penalty.
Nic Fitisemanu scored Nottingham's only try, converted by Neil Stenhouse.
Quins will face Bedford in the final at Twickenham on 9 April. The Blues beat Exeter 37-35 in the other semi-final.