That record looked under threat early yesterday, after they trailed 18-12 at the end of the first quarter.
The hosts got quality early contributions from shooters Te Paea Selby-Rickit and Jhaniele Fowler-Reid, thriving on tidy work from the Steel feeders.
However, Mystics midcourters Laura Langman and Serena Guthrie slowed the Steel's start, with a lift in their defensive efforts notable as the visitors surged back into contention.
The Steel took a tenuous 33-32 lead into the main break - an advantage they relinquished in the third quarter and failed to reclaim, despite a late run which tightened the contest.
"I'm really proud of the fact we could hold them off because they can score fast," said coach Fuller.
Goal shoot Cathrine Latu (44/49) was a standout for the visitors, showing strong movement and accuracy under the Mystics hoop.
"She was really amazing and I'm lucky to have such a stable option under [the hoop]," said Maria Tutaia of her partner in the circle.
Fowler-Reid (43/45) put up her unusual incredible numbers and Tutaia (19/24) and Selby-Rickit (15/17) also contributed to the high-octane display.
The home side came from four goals down to level the scores in a frenetic run to the line, but crucial turnovers proved their undoing.
"We brought it back but they're a quality side and we just couldn't finish it out there," said Steel captain Wendy Frew. "It really hurts but hopefully we can come back strong."
The loss put a dent in the Steel's playoff hopes.
Janine Southby's side will now have to rely on other results going their way to finish in the top three in the New Zealand conference.
Meanwhile, Fuller realises her side need to keep on improving.
"Things change overnight in this competition and it's absolutely brutal," said Fuller.
"We've got to keep building and go up another gear going into finals. We're still not the finished product at all."
The Mystics host the Vixens next week to finish their regular season, while the Steel will travel to Queensland to take on the table-topping Firebirds.
Steel 61 (J. Fowler-Reid 43/45, Te P. Selby-Rickit 15/17, B. Leaver 3/5)
Mystics 63 (C. Latu 44/49, M. Tutaia 19/24). Q1 18-12, Halftime 33-32, Q3 46-50.