It was a close-run contest with Australia finishing strongly and a contentious restart just as the final hooter sounded but New Zealand won a key decision and were able to clear the ball from a scrum to win.
It was the first time they completed four tournament wins at the same venue, and included a hat-trick of wins. Most importantly, in beating Spain 17-7 in their quarterfinal, the Black Ferns secured their place at next year's Tokyo Olympic Games.
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New Zealand will go into the final tournament of the HSBC Series in Paris next month on 92 points, 12 ahead of the United States, Canada on 78 and Australia 74.
New Zealand captain Sarah Hirini said after the win, "I'm really proud of the effort the girls have put in over the last few days. Our goal this season was to qualify for the Olympics and that's for all the girls back home who are training really hard and our coach back home as well.
"Australia are an amazing team and every time we play them we have to play our best as it's a tough match. I'm just so proud of the girls and how we dug in," she said.
As per tradition, the #BlackFerns7s celebrate that Cup Final with a HAKA! #Canada7s
Australia scored first in the final through Ellia Green who broke out from her own 22m area when catching Michaela Blyde off her line and was too fast over 80m.
However, New Zealand struck back on the back of a strong breakout by Shakira Baker down her wing. The ball was moved across field before coming back where the player of the final Tyla Nathan-Wong linked with Sarah Hirini, who scored to get New Zealand on the board.
The second try followed moments later when a tap penalty was moved wide for Nathan-Wong to reverse-pass to Niall Williams who cut through and scored.
Just before halftime some clever play by Australia's Charlotte Caslick opened up the Black Ferns' defence and Emma Tonegato put her speed to use to score and make the halftime score 14-10 to New Zealand.
Australia were unable to capitalise on Nathan-Wong's second half restart not going 10m and it was from a mid-half scrum that Kelly Brazier provided the set-up work which freed Hirini who then found Nathan-Wong on hand and she employed her fend to push off the tackle and run 40m to score.
That proved vital as moments later Williams threw a wild pass in-field that fell short of Ruby Tui and Green was onto the ball in a flash to score. From the restart a knock-on was ruled giving New Zealand the scrum feed from which they kicked the ball out to end the game.
FT | The #BlackFerns7s take out the 2019 @CanadaSevens Cup Final!
Earlier, the Black Ferns scored from the kick-off of their semifinal against the United States with the ball won and moved to the left where Blyde cut back infield to claim the try.
Moments later, Tui was dropped in a dangerous tackle, on the unforgiving Langford pitch by American Alev Kelter. The American was immediately given a red card.
New Zealand took time to recover and it was after being hurt in a collision that Brazier got up in time to station herself on the end of the line to score her first try.
The Americans struck back from the restart when Naya Tapper took the blindside route from the kick-off maul. She beat Blyde and Williams with her speed and opened the scoring for the USA.
From the restart Blyde unleashed a crossfield assault, sidestepping her way from the left to right flank and when the ball was released by Nathan-Wong to Brazier on the wraparound she scored her second try to give New Zealand the lead at halftime 19-5.
With the one-woman advantage New Zealand dominated possession – at one stage they had made 63 passes to one by the Americans – but they had to compete with dogged American defence in the second half. They managed only the one try, to Brazier.
The Americans got one back when Kristi Kirshe put a big fend on Terina Te Tamaki to run 70m for the final try in New Zealand's 26-12 win.
Starting the day with their quarterfinal against Spain, the Black Ferns opened the scoring with some determined play by Tui who broke from a ruck, and while stumbling on her way to the goalline, she unleashed a roll and a dive to get the ball down.
Brazier's defensive work helped snuff out two Spanish scoring chances before Nathan-Wong split the defence with a dummy to score.
The Spanish showed their own defensive capabilities when denying Brazier and Shakira Baker scoring chances and Maria Garcia was rewarded with a try for Spain. Alena Saili was also held up close to the line but from the recycle Sarah Hirini fed Dhys Faleafaga on the right for the try.
"Every time we've played them they've tested us. They're great around the ruck, they're strong ball carriers. But our girls have stepped up, they've learnt a lot from Japan and they're going really well at the moment," Hirini said.
After @BlackFerns tight win, it keeps them at the top of the @HSBC_Sport Women's Sevens Series standings pic.twitter.com/O2iTy3Fl6E— World Rugby Sevens (@WorldRugby7s) May 12, 2019