Harris hit a competition record-equalling six sixes in her 42-ball 89 not out, but was nearly upstaged by her former Australian captain Lanning, who hit five of them before being dismissed for 85 off 51 balls.
Her departure sealed London Spirit's victory over capital rivals Oval Invincibles by 17 runs.
The match was the first half of a double-header at Lords to kick-off the controversial competition, in which both sides receive 100 balls bowled in 'sets' of five, with the men, including Spirit's David Warner, following.
It was a stunning opening with a competition record 15 sixes in all.
Harris led the defending champions to 5-176, the second highest score in the competition's history.
The Queenslander was brutal on former Australia teammate Amanda Jade-Wellington, who went for 38 off her 15 balls - but she did have Harris dropped on 22.
The other Australians in Spirit's team fared less well. Georgia Redmayne, opening the innings, struggled to a six-ball duck. Charli Knott, recruited late to replace the unavailable Indian star Deepti Sharma, made one off four.
Harris put on 100 with Englishwoman Cordelia Griffith (50 off 29), a team record, in 52 balls.
"I loved it out there," she said. "When you have a wicket like this, you want to cash in as a batter."
On the secret to her clean hitting she suggested "genetics maybe?" before focussing on good prep, technique and an unconventional diet for an athlete.
"Three gym sessions a week. Your handspeed as well. Your feet don't have to move well but a still base and you can time balls for six with your hands.
"A few burgers in there. I have been living on dumplings since I have been over in England and it seems to be working! No Harris is a small human being, so I will take it."
"She is very powerful and makes it look easy," said Lanning of Harris. "Fair play to her, she was too good.
"They set a great total and we were a bit behind. I couldn't get going early on. Once I found some tempo, I had some momentum going."
True enough, prior to being out Lanning went 6,4,4,6 and looked about to mastermind a heist over the team she played for last season.
There are 16 Australians in the women's competition in all, with all but one of the eight sides having an Aussie.
This is the last season solely under the control of the England and Wales Cricket Board with large chunks of most teams sold to private owners, half of them Indian Premier League clubs.
This has raised $A1 billion for the sport in England, though that hasn't quelled criticism from traditionalists who fear it threatens the county structure and annexes the key summer month of August.
However, besides the cash The Hundred has succeeded in its aim of attracting a new audience - this midweek afternoon women's match drew 15,640 to Lord's.
Australian officials, pondering the future of the Big Bash League, will have taken note.
AUSTRALIAN WOMEN IN THE HUNDRED
Ellyse Perry, Megan Schutt, Georgia Voll (Birmingham Phoenix), Grace Harris, Georgia Redmayne, Charli Knott (London Spirit), Beth Mooney (Manchester Originals), Phoebe Litchfield, Annabel Sutherland, Georgia Wareham (Northern Superchargers), Amanda-Jade Wellington, Meg Lanning (Oval Invincibles), Ash Gardner, Alana King, Heather Graham (Trent Rockets), Jess Jonassen (Welsh Fire).
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