Wellington eschewed a couple of golden opportunities, which would have made for a more comfortable night, as they allowed Macarthur to take the initiative for long periods.
But after a dismal run of form the Phoenix got the job done, marking their third finals appearance in four seasons under departing coach Ufuk Talay.
They will need to improve considerably to go any further – with a trip to Adelaide for the elimination final next week – but at least this victory will ease some pressure and allow Talay an appropriate finale.
Six weeks ago, after a home win over Sydney, the Phoenix were in the hunt for a top-two spot but they have dived dramatically since, with only one point from their previous five matches, conceding 17 goals in the process.
That left them on the edge and led to another nervy affair. Wellington have dropped more points from winning positions this season than any other team and that scenario looked possible again, as they couldn’t build on the early lead.
But they did enough to hang on, showing plenty of grit, albeit against a fairly toothless Macarthur side that lacked much cutting edge in the final third.
Wellington made a perfect start. Zawada’s opportunity came after Yan Sasse released David Ball, with the Polish striker dispatching the rebound after Filip Kurto had parried the Englishman’s effort.
That took Zawada’s season tally to 15, a total only exceeded by Jeremy Brockie (16, 2012-2013) and Roy Krishna (18, 2018-19) in club history.
From there the Phoenix could have put the game out of sight. Callan Elliot was denied by a brilliant Kurto block, after a delightful combination with Ball, though the young defender looked odds-on to score.
Soon afterwards the ball fell to Kosta Barbarouses from a corner but he dragged his shot wide. In the conditions, they were costly misses and the home side controlled the rest of the half.
They didn’t threaten too much- despite a huge possession advantage – but Alex Rufer and Scott Wootton managed crucial blocks, while goalkeeper Oli Sail had to be alert as the ball skidded and skimmed off the turf.
Wellington rarely pressed, content to sit deep in their own half, which was a risky strategy at times. But they started to find their groove again after the break and Zawada should have doubled the lead in the 61st minute, flashing his angled shot wide after being set up well by Sasse.
Josh Laws was brought on for the Brazilian in the 66th minute, as the visitors switched to a back five, holding their ascendency until the end, with their first clean sheet since mid-March as a bonus.
Phoenix 1 (Oscar Zawada 11′)
Macarthur 0