Brisbane were beaten 2-0 by second-placed Sydney in their final match of the regular season at Moreton Daily Stadium on Saturday.
Goals from Kosta Barbarouses and Harry Van der Saag opened the door for the Mariners to move above the Roar and take third place, an opportunity they grabbed with both hands.
Jack Clisby struck in the first half and Marco Urena sealed the victory in stoppage time at Central Coast Stadium.
Alen Stajcic will pit his wits against fellow former Matildas coach Ante Milicic in an all-New South Wales clash next Saturday.
The Roar will have an extra day to prepare for a home showdown with Adelaide United a week on Sunday, when a place in the semi-finals will be up for grabs.
Newcastle Jets moved off the bottom of the table courtesy of a 1-1 draw with Perth Glory, A Jonathan Aspropotamitis own goal giving them a point after Bruno Fornaroli opened the scoring.
That point moved the Jets above Melbourne Victory, while Perth remain ninth.
Western Sydney Wanderers will host Macarthur FC in the 2020-21 season opener on December 27, it was revealed on Tuesday.
The other opening games will see Western United host Adelaide United, Wellington Phoenix visit Brisbane Roar, Sydney FC take on Melbourne City and the F3 Derby between Central Coast Mariners and Newcastle Jets.
The opening round would seem like just another game, but history shows otherwise.
With the help of Opta data, we assess just what round one means in the A-League.
Opening loss and trophies become difficult
Incredibly, only twice in A-League history has a team that lost in round one gone on to be crowned champions or premiers of that season.
The first instance came in 2011-12, when the Mariners were edged by Brisbane in round one, but went on to win the Premiers' Plate, finishing two points clear of the Roar.
Melbourne Victory were the second, going on to be crowned champions in 2017-18 despite a 1-0 loss to Sydney FC in round one.
In all, six of the nine teams to do the A-League double of being crowned premiers and champions in a single season have done so far after winning in round one. The other three drew. Of the 15 champions, seven have won and seven have drawn, to go with Victory's 2017-18 defeat, in round one. Nine of the 15 premiers have won in the first round, alongside five draws and the Mariners' loss.
Round one looks hugely important in the A-League.
Fast-starting Sydney, Glory woes
Sydney have scored more goals (21) in round one games than any other team in the competition, while earning the most points per game (1.7) of teams to have featured in at least five seasons.
The Sky Blues have lost just two round one matches in their history, and the most recent of those was in 2012-13. They face a huge test to begin 2020-21 season, hosting Melbourne City in a Grand Final rematch at ANZ Stadium.
On the other hand, Perth Glory have lost more games in round one than any other team in A-League history with seven.
In contrast to Sydney, Perth are winless in their past five openers, their last win coming in 2014-15.
The 2019-20 A-League campaign has been suspended since March due to the COVID-19 crisis, but Australia's premier football competition is set to restart on July 16 followed by a five-game finals series – the Grand Final to take place on August 23.
A derby between Melbourne Victory and Western United – originally scheduled for AAMI Park in Melbourne – will be played at a stadium still to be determined due to a spike in coronavirus cases in the state.
Six venues will be used in New South Wales and Queensland with the potential for more to be added subject to government regulations – ANZ Stadium (NSW), Bankwest Stadium (NSW), Central Coast Stadium (NSW), McDonald Jones Stadium (NSW), Jubilee Stadium (NSW) and Cbus Stadium (QLD).
"Over the past three months all stakeholders have been working hard together with one goal in mind – To finish what we started," FFA's Head of Leagues Greg O'Rourke said on Wednesday.
"We know the COVID-19 environment has been very difficult for many people in our community and we hope that delivering an extravaganza of matches will allow our fans to basically see a game everyday will be a unique experience for those who have stood by us.
"As we are a truly national game, the current border controls means that some of the match day venues may need to change, however we have secured venues in both a NSW Hub model and a hybrid hub model which has most games in NSW but allows for a few games in other states.
"Whilst we don't see the draw changing, the planning we have undertaken provides us with agility to shift between certain states if required. This version of the draw displays our current venue plan.
"We will continue to work with the Federal and State governments to ensure the health and safety of our players, coaches and other stakeholders and have detailed and practical protocols in place for all parties involved in training and match days.
"I am excited to see us kick off the restart and ultimately finish off what we started last October, with our priority always being to be in a position to crown our Hyundai A-League premiers and champions for this season."
Defending champions Sydney FC top the table by eight points through 20 matches, though second-placed Melbourne City have played three games less.
The Jets were in A-League action on Monday in what proved to be the final game before the season was suspended due to the pandemic.
In a statement on Saturday, Newcastle confirmed a player had tested positive for COVID-19, but was feeling fine.
"Newcastle Jets can confirm that a player in its Hyundai A-League squad has returned a positive test for COVID-19," a statement read.
"In accordance with relevant protocols, NSW Health has been notified of the case by the club and the correct procedures have been followed throughout.
"The player and his family are in good health, and currently in quarantine in accordance with NSW Health protocols.
"The health and wellbeing of our players, officials, and the wider community remains our highest priority in this difficult time.
"As per advice from NSW Health, our playing squad are closely monitoring their health and will isolate themselves if they experience any symptoms.
"All players and staff beyond the player have been checked for their risks and will be overseen, and guided, by the team medical staff as they liaise directly with the Public Health Unit. Self-isolation has been commenced for those that require it."
There have been more than 597,000 coronavirus cases worldwide, with the death toll climbing above 27,300.
Australia has seen more than 3,570 cases, including 14 deaths.
The Mariners finished third last season before failing to advance to the semi-finals in the post-season but have ended the first round of 2021-22 fixtures on top of the table.
Joshua Nisbet squeezed a low finish past Newcastle goalkeeper Jack Duncan shortly after half-time, and a second away goal soon followed through Jacob Farrell's thumping header.
Angus Thurgate's superb cross teed up substitute Valentino Yuel 12 minutes from time to set up a tense finish, but the Jets could not recover a first point of the season, slipping to a second consecutive home defeat in the F3 derby for the first time in A-League history.
The spoils were then shared between Macarthur and Wellington Phoenix in a 1-1 draw that extended the nominal away side's record unbeaten run to 12 matches.
Macarthur pipped their opponents to a Finals place by a single point last term, but they were forced to play in Newcastle due to the poor standard of their Campbelltown Stadium pitch and then trailed to Gary Hooper's penalty midway through the first half.
Lachlam Rose's 61st-minute finish beat Oliver Sail to get Macarthur back on terms, although there were grateful to Tomislav Uskok for a goal-line clearance in the closing stages.
Dimitri Petratos' double lifted the Jets to a deserved win in wet conditions at McDonald Jones Stadium.
With Carl Robinson, who will take over as Jets head coach on Monday, watching on from the stands, Newcastle recorded just their third victory of the A-League season.
They remain bottom of the table with 10 regular-season games remaining, but are now nine points behind sixth-placed Brisbane Roar, who hold the last finals place.
Petratos' powerful finish put them ahead before the attacker's corner found Nikolai Topor-Stanley unmarked at the back post to make it 2-0.
However, Central Coast found a way back into the contest from two set-pieces either side of half-time as Ruon Tongyik and Jack Clisby headed home.
Another well-taken finish from Petratos restored the Jets' lead before a Kim Eun-sun own goal and they survived late on despite Chris Harold's fine strike on debut for the Mariners.
The Jets ended a two-game winless run against the Mariners and the victory was their sixth in the past eight meetings between the clubs.
