Newcastle just scored vs Sydney.
If Sydney don't win we only need a draw or win next week to guarantee 2nd, if Sydney win vs the Jets a draw next week would mean Sydney would be 2nd.
2nd is straight through to the semi (and I assume a home one), whereas getting <= 3rd means an extra match to win to win the title.
Edit - I forgot about Adelaide.... if they win both their games they will finish above us as their goal difference is better than ours, so they need to drop a point for the above to apply. I'm assuming Melbourne will win of their next 2 matches and finish 1st.