The Central Coast Mariners have secured the Premiers' Plate through a 2-1 victory over Wellington at Westpac Stadium on Sunday.
The Mariners entered the match knowing a win would secure them their second minor premiership but that a draw or loss would leave the door open for 2010/11 champions Brisbane Roar.
The Phoenix needed victory by three clear goals to take third spot after Shane Smeltz's heroics for Perth Glory the previous night.
But against a team they had scored just one goal against and had not beaten this season that outcome never looked likely for Wellington - although Leo Bertos' 80th-minute free-kick ensured a tense final 10 minutes for the visitors.
But in reality, when Sutton headed the Mariners in front just before half-time, the outcome for both teams was effectively sealed.
Ibini's well-deserved second early in the second half secured the regular season silverware for the Mariners who have sat atop the table for much of the campaign, leading by 11 points at one stage.
Central Coast will travel with confidence to Suncorp Stadium for Saturday's major semi-final first leg against the Roar, while Wellington – like the Glory – await the result of the Newcastle-Sydney match to see if they will play either of those teams or Melbourne Heart in next week's elimination finals.
Mariners coach Graham Arnold started strikers Ibini and Sutton after resting them from the XI that played against Nagoya Grampus in the AFC Champions League midweek.
It proved to be a masterstroke as Ibini looked lively from the start, finding his way into the Phoenix box with regularity and it was no surprise that he was the catalyst to Sutton's 45th-minute goal.
The 19-year-old striker gathered a poor clearance kick from Andrew Durante and raced unchallenged towards the top of the box where he picked out Oliver Bozanic, who had made a good run down the left. Bozanic then fired in the cross which Sutton glanced beyond a diving Mark Paston.
Ibini had had an earlier chance to put the Mariners in front when he completely outpaced Ben Sigmund to get into the Phoenix's six-yard area but Paston smothered his attempted shot.
That attempt in the 33rd minute was sandwiched by chances for the Phoenix.
Paul Ifill, who started despite suffering from flu all week, saw his shot come straight back off Mariners goalkeeper Mathew Ryan, Dani Sachez's strike then hit Patrick Zwaanswijk before Ryan batted away another effort from Chris Greenacre.
Greenacre had an even better opportunity just minutes later when an Ifill pass split the Mariners defence but the veteran Englishman – in a one-on-one with Ryan – found the goalkeeper's left leg rather than the back of the net.
Manny Muscat then forced another save from the Mariners goalkeeper late in the first half.
The visitors continued to dominate in the second half and it was no surprise when the second goal came.
Durante, who had an unhappy 100th appearance for the Phoenix, coughed up possession again and the lively Michael McGlinchey ran virtually unchallenged deep into the opposition half before threading a pass through to Ibini, allowing the striker to coolly slot it into the bottom corner.
With third spot well out of reach and Friday's play-off match to consider, Phoenix coach Ricki Herbert turned to his bench bringing on Mirjan Pavlovic for Greenacre, Nicky Ward for Dani Sanchez and Alex Smith for Tony Lochhead.
It brought some much-needed spark to the home side's attack and as they started to press forward with more intent McGlinchey fouled Vince Lia and Bertos curled a long-range free-kick over the Mariners defence and a leaping Ryan to give the home side some hope.
But it was too little too late and the Phoenix will now have to lift themselves for the finals series after end-of-season back-to-back losses.