The Bulldogs kicked away in the third stanza and then consolidated in the fourth to run out 15.16 (106) to 9.13 (67) winners.
Mitch Banner booted five for the winners.
West Coast’s Daniel Kerr racked up 31 disposals in the 15.13 (103) to 10.9 (69) win, but was reported in the third term for high contact on the Lions’ Simon Moore.
The Sharks were switched on early, holding a four-goal lead at the first change, with their forward pressure key to their early success.
Subiaco did make a charge in the second term, bringing the deficit down to five points.
But with their season on the line, the Sharks poured on the pressure to run out comfortable winners.
Ryan Lester-Smith was at his crafty best, bagging four goals, while former Fremantle defender Antoni Grover also booted four.