City thrashed Perth Glory 5-1 on the road, taking an immediate grip on the match with goals from Taylor Otto and Bryleeh Henry in the opening six minutes.
Though Glory pulled a goal back with a 12th-minute penalty from Susan Phonsongkham a second Otto goal restored City's cushion after 26 minutes.
Golden Boot leader Holly McNamara added her 15th of the season five minutes before half-time to send the visitors into the break with the title all-but confirmed.
In a quieter second half Leticia McKenna completed the rout in the 68th-minute.
Earlier on Friday, underlining their decline since last season's grand final, Sydney FC lost 2-1 at Adelaide United to conclude their worst season since the league began in 2008-09. Former Sydney player Fiona Worts struck twice after Madeleine Caspers had opened the scoring.
Melbourne have gone unbeaten both at home and in the Asian Champions League since their grand final defeat to Sydney, a 27-match run.
"Words can't describe the feelings that are going through my body at the moment, I am super proud," said City coach Michael Matricciani, who took over at the start of the season when Dario Vidosic left for Brighton & Hove Albion.
"One trophy down, to go undefeated - I couldn't ever imagine that," added Matricciani to Paramount+. "It is a true testament to the determination, focus and quality of these girls. All credit goes to them."
There was never any chance of City losing the Invincibles tag at the Sam Kerr Football Centre with Otto heading in a near-post corner then Henry sliding in a Loudes Bosch pass in the opening minutes.
After Phonsongkham's penalty, given for handball, Otto headed in another Alexia Apostolakis corner at the near post before McNamara completed a slick passing move that typified City's attacking elan this season.
"I haven't seen it back yet but watching it live was pretty special," said Matricciani, as he shook off the effects of being given an unexpected ice-bath by his players.
"This is something we have been working on a lot for the last six-seven weeks, combination play around the box, especially when teams are sitting seven, eight, nine players behind the ball, how we can unlock that. We've been getting close and tonight that was a super goal."
The icing was added by McKenna with a long-range free-kick.
"These moments are very special." added Matricciani. "I'm really pleased, after the season I might enjoy it a bit more, but we've still got a lot of football to play."
Together with runners-up Melbourne Victory, City now go straight into the second stage of the play-offs. Adelaide, Canberra United, Central Coast Mariners and Western United will contest the first stage with the fixtures to be determined by the rest of the weekend's game.
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