In a game that felt erringly familiar to a bunch of the Steel's losses this season, the home side led for more than half the match, only to come up short when it mattered most.
The two goal loss to the New Zealand conference leaders means the Central Pulse can knock the Steel out of the third and final playoff spot if it beats or draws with the Magic in Hamilton tonight.
After trailing by four goals inside the last three minutes, it looked like the Steel might snatch a draw for the second straight week on the back of a late surge.
However, up 62-61 with 45 seconds left, the Mystics ground the clock down, before shooter Cathrine Latu iced the game with one last goal as time expired.
Steel coach Janine Southby rued a lack of composure at crucial times for the loss.
''We're all pretty disappointed,'' she said.
''I think we had opportunities again, but under pressure we just didn't make some good decisions. We had a run of the centre passes for most of the fourth quarter. But one silly pass here and they got a couple of tips on the ball and that was it.
''It's one of those frustrating ones. So close, but it may as well have been 10 goals.''
Southby's side made a good start to the match, jumping out to an 18 12 lead at the end of the first quarter.
Shooter Jhaniele Fowler Reid, who landed 43 of her 45 shots on goal, made a spectacular play to finish the first quarter as time ran out. She gathered a terrific pass from beyond halfway by Gina Crampton, and somehow landed the shot off balance as she was falling out of bounds.
The Steel led by as many as seven goals early in the second quarter, before the Mystics began crawling their way back into the game.
Up 32-28 inside the last three minutes of the first half, the Steel stumbled when defender Phoenix Karaka had a pass picked off by Mystics defender Kayla Cullen.
That sparked the visitors into a four goal run to tie the game up, before Fowler Reid put the Steel up by a lone goal at the half.
Southby replaced defender Jane Watson with Storm Purvis, who missed the previous two games with an ankle injury, late in the second quarter. She did not waste any time making an impact, almost immediately intercepting a Laura Langman pass into the circle.
Goal attack Brooke Leaver was also injected into the game for Te Paea Selby Rickit in the third quarter, but it did not have the same impact as in past games.
Instead, the Mystics scored six straight goals on their way to a handy fourth quarter lead to help set up their seventh win of the season.
The Steel must now travel to Brisbane to take on the Queensland Firebirds, the top side in the Australian conference, on Sunday.
Southby admitted she would be keeping an eye on the Pulse v Magic game tonight, and was remaining optimistic about her side's chances of making the playoffs.
''We have got nothing to lose in Brisbane,'' she said.
''If we go out there and do our own jobs and have some fun then anything's possible. That's what we have got to keep working for.''
ANZ Championship
The scores
Northern Mystics 63
Cathrine Latu 44/49, Maria Tutaia 19/24
Southern Steel 61
Jhaniele Fowler Reid 43/45, Te Paea Selby Rickit 15/17, Brooke Leaver 3/5
Quarter scores: 1st, 18-12; 2nd, 33-32; 3rd, 46-50.
