The win means the Firebirds leapfrog the Steel into fourth place, but both sides are on 12 points with six wins from 11 matches.
The West Coast Fever is still in the running after it beat the New South Wales Swifts in Sydney on Sunday.
The Fever is on 10 points with five wins from 11 matches and joins in a three-way battle to secure the remaining play-off spot.
The Waikato Bay of Plenty Magic, Melbourne Vixens and Adelaide Thunderbirds have secured semifinals berths.
When the Steel looks back at the tape to explain the loss, aside from having a few impolite words for the officials who made some baffling calls which left the commentary team scratching their heads, it could probably pinpoint one moment with just under three minutes remaining which cost it dearly.
The visitors were trailing by two and Donna Wilkins had put up a shot which rolled three-quarters of the way in, then somehow escaped the laws of physics and the clutches of the net.
The Firebirds moved quickly into attack and scored.
Instead of trailing by one goal, the Steel was behind by three.
That was it.
The chance was gone.
It is hard to fault Wilkins, who played superbly, landing 32 of her 35 attempts on goal.
But the Steel now faces a tough road to reach the semifinals with a match against the third-placed Thunderbirds in Dunedin on June 29 and the Swifts in Invercargill on July 4.
Both games are at home, whereas the Firebirds play the Northern Mystics in Auckland and the Fever in Perth.
Steel coach Robyn Broughton opted to start with Megan Dehn despite the Australian only joining the squad two weeks before when shooter Daneka Wipiiti confirmed she was pregnant.
The experienced player took a little time to find her feet.
The ball slipped through her hands once or twice and the odd shot looked wobbly.
But her extra mobility helped the Steel stretch the Firebirds defence.
Laura Geitz and Peta Stephens over-committed on occasion, allowing the Steel to pop in unguarded goals.
That helped Dehn settle and, as she warmed to her task, her shooting improved.
With Wipiiti absent, the pressure went on Wilkins to shoulder more of the scoring responsibilities.
The dual basketball and netball international has largely played second fiddle this season, content to feed Wipiiti.
But she lifted her game and the new combination equipped itself well.
Still, the Firebirds went into the half-time break with a 26-25 lead.
Lanky Jamaican shooter Romelda Aiken got the better of her opponent, Megan Hutton. Aiken scored 48 of her side's 52 goals and definitely won the points battle with Hutton.
Firebirds 52 (Romelda Aiken 48 from 59, Alissa Castrisos 4/8) Steel 50 (Donna Wilkins 32/35, Megan Dehn 18/21)
