Be sure to set your difficulty in WRC 8 gameplay settings to Authentic via:
Main menu->Options->Gameplay settings->Configure->Difficulty->"Authentic".
(Seems to be important when connecting.)
Also set your damage effects (probably optional)
Main menu->Options->Gameplay settings->Configure->Damage effects->"Visual only".
Setup:
Main menu->Competition->Create lobby
Server will be a:
- Lobby visibility: Public game,
- Damage effects: Visual only,
- Category: WRC,
- Special Stages: "Stage only"
- Rallies: "Rally Sweden" (-> Torsby 5.67km)
Quit online mode after winning the 1st Stage.
Change your settings back to easy via:
Main menu->Options->Gameplay settings->Configure->Difficulty->"Easy".
Select solo quick play, and pick any stage and win that stage as well, via e.g.
Main menu->Solo->Quick Play->Sweden->Torsby (5.67km)->WRC->...
Once you finish the stage, the "Race master" achievement should unlock.