Mehmet struck four minutes from time after Brett Emerton (54) and Bruno Cazarine (72) had put the hosts ahead.
However, they could not draw level and squandered the chance to cut the gap on leaders Central Coast Mariners.
Newcastle Jets leapfrogged Melbourne Heart into fifth with an emphatic 3-0 victory.
Jeremy Brockie put the Jets ahead with a goal in the 27th minute and Ryan Griffiths doubled the lead two minutes after the break.
Michael Bridges completed the scoring while Heart's misery was compounded when Curtis Good was sent off in the final minute.