South Perth advanced to the WA Rugby League grand final, brushing aside North Beach 37-18 at George Burnett Park on Saturday.
With the game locked at 18-all after 70 minutes the Lions ran in three unanswered tries in the final 10 minutes.
North Beach flirted with control during the game but whenever they looked like breaking the game open, handling errors stopped them in their tracks.
Lions halfback Mark Porges was man of the match and capping off a memorable day with a field goal as his side showed they are able to cope under pressure.
They will be hot favourites going into the grand final.
In the minor semi final Fremantle ended Willagee's season with a 34-16 victory at Ken Allen Field and will face North Beach at Charles Riley Reserve.