Knowing they had finished first for a third consecutive season before the game, Melbourne wanted to end their regular campaign on a high with finals and a Women's AFC Champions League semi-final upon them.
But it was Newcastle who threatened to spoil their plans when their top scorer Melina Ayres drew first blood at Maitland Sports Ground on Sunday.
City had hit the crossbar three times while trying to find their the equaliser, until forward Aideen Keane poked a driving cross from Karly Roestbakken into the top right corner in the 72nd minute.
Melbourne didn't want to settle for a draw, and in the 97th minute Roestbakken lofted another ball into the box and found Turner, who headed it into the net.
Victory extended City's unbeaten streak across all competitions to eight games, while also maintaining their undefeated record against the Jets on the road.
Melbourne were missing several stars, with Matilda Holly McNamara concussed, striker Chinaza Uchendu suspended, and other players on Young Matildas' duty.
"That was very hard. They kept coming back. That was very physical," midfielder Leticia McKenna told Paramount+.
"We knew they were going to come at us, and we just had to keep fighting, keep knocking on that door, and keep going forward."
Newcastle already knew even a win wouldn't be enough to make the top six, and the result ends their ninth-placed campaign on a low note.
"That pretty much sums up our season. We've fought so hard in games, and we've been so close to being where we want to be," Ayres said.
"It's positive signs that we are matching it with the best. Hopefully that means finals for us next year."
City came within a whisker of scoring first when McKenna curled a free kick into the crossbar before the follow-up by Taylor Otto was hit wide.
With scores locked at 0-0 at halftime, it took less than two minutes for Ayres to find the net when fellow forward Kelli Brown found the 26-year-old, who unleashed a shot into the goal.
Melbourne continued to sniff, but two shots by McKenna and Leah Davidson clattered into the crossbar.
The visitors were finally rewarded when Keane netted the equaliser, before Turner scored in injury time to steal the victory in the final game of the competition's regular season.
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