Ibini's 35th-minute goal came via a Trent Sainsbury throw-in which saw Nick Montgomery tap the ball into the path of the striker, who still had work to do before a cool left-foot finish gave the home side the points.
The Mariners, now on 48 points, cut the gap to leaders Western Sydney Wanderers to five points and still have an outside chance of retaining the Premiers Plate.
The Roar missed a chance to move into the top six and are still two points behind sixth-placed Newcastle, although they do have a game in hand on the Jets.
Wellington Phoenix picked up a rare win, 2-1 away to Perth Glory, but remain bottom of the league.
Paul Ifill and Stein Huysegems gave the Phoenix a 2-0 lead before Ryo Nagai pulled a goal back.
Wellington are now level on points with Melbourne Heart and only one behind Perth and Brisbane, but have played a game more than all three teams.