Central Coast Mariners sealed second place in the table and a second chance in the A-League play-offs with a 3-1 win over Gold Coast United at Skilled Park.

Needing just a point to confirm their position as runners-up to Brisbane Roar, Central Coast opened the scoring after 13 minutes when Bernie Ibini-Isei rifled home Josh Rose's cutback.

Mustafa Amini doubled the visitors' lead five minutes before the interval when the young midfielder smashed Adama Traore's clearance past goalkeeper Glenn Moss.

Substitute Mitchell Duke then put the result beyond doubt in the 67th minute when one-on-one with Moss after Oliver Bozanic had sent him clear.

Central Coast now face Brisbane Roar in the major semi-final with the losers guaranteed another opportunity to reach the Grand Final.

Wellington Phoenix were unable to secure their play-off place after losing 2-0 at Sydney FC.

Following a goalless first half, Sydney took the lead thanks to a huge slice of luck ten minutes after the break at Sydney Football Stadium.

Nick Carle earned a penalty after being brought down by James Muso in the box but fired his spot-kick straight at Phoenix goalkeeper Danny Vukovic.

The midfielder did exactly the same with the rebound but fortunately it hit the goalkeeper, deflected off Nick Ward's head and ended up in the back of the net as an own goal.

Brendan Gan then wrapped up victory when he converted Shannon Cole's pass in the 69th minute.