Canada parlayed that momentum into a 40-12 blowout victory over Mexico later on Saturday to go undefeated on the day.
The Canadians are slated to play the U.S. in Sunday's semifinals.
One-on-one tackling, which hurt the Canadians at last week's World Series event in Vancouver, was rectified with strong team defence at Commonwealth Stadium in a 7-7 draw with the Brits.
The visitors struck first 57 seconds into the contest when Megan Jones handed off to speedy Jasmine Joyce for the try.
Seconds later, Jones caught and took down Charlottetown's Alysha Corrigan, who looked as though she might even the match.
Ottawa's Olivia De Couvreur broke through coverage on the final play of the first half for the try, with Olivia Apps of Lindsay, Ont., converting to even the match.
Earlier, Renee Gonzalez of Toronto couldn't have been better with her timing, scoring tries in the opening minute and second half to provide the Canadian women with momentum en route to a 26-26 tie against the U.S.
Sabrina Poulin came off the bench to pull Canada within two points before Apps converted for the third-seeded Canadians, who rebounded from a pair of losses to the Americans a week ago at BC Place Stadium.
Canada's men made it 13 wins in as many World Series meetings against Hong Kong, opening play Saturday with a 21-12 victory. Josiah Morra, team captain Phil Berna and Brennig Prevost had the tries. They followed with a 47-0 rout of Mexico.
After Gonzalez gave the Canadian women an early lead, Summer Jones went to work for the No. 2 Americans. First, the Los Angeles athlete fended off two would-be tacklers for her team's first try before racing through the open space in the middle of the field for the lead.
Steph Rovetti split a pair of Canadian defenders for another try and 21-7 U.S. lead entering halftime.
Emma Chown of Barrie, Ont., answered inside the first two minutes of the second half with a penalty as Jaz Gray was sent off and the U.S. was down to six players.
Gonzalez scored her second try of the match with 4:12 remaining but the conversion was missed.
Jones made it 26-19 with 1:53 left on the clock, using a stutter step to freeze the Canadian defence before outrunning at least three opponents.
The women's competition features just four teams: Canada, Britain, the U.S. and Mexico.
The "Fast Four" competition format sees the teams play each other before the top two decide the gold and the other two meet for third.
Britain won the women's event in Vancouver, downing the U.S. 34-12 in the final. The Canadian women placed third, blanking Mexico 48-0.
Canada's men were drawn in Pool A with South Africa, Mexico and Hong Kong. They entered play Saturday fresh off a sixth-place finish last Sunday in B.C., where the World Rugby Seven Series returned after a lengthy pandemic-prompted hiatus.
Thomas Isherwood of Okotoks, Alta., delighted the home crowd with a team-leading three tries against Mexico while Anton Ngongo and Ciaran Breen had two apiece.
Matthew Percillier added four converts and Prevost a pair.
Only seven of the men's core teams are taking part in the Canadian events with New Zealand. Fiji, Australia, Argentina, Japan, France and Samoa among those missing due to pandemic-related travel restrictions.
The 2022 World Series season will start with back-to-back combined events in Dubai. The first, Nov. 26-27, will be held behind closed doors while the second, Dec. 3-4, will see fans in attendance at the Sevens Stadium.
Attendance at Edmonton's Commonwealth Stadium is limited due to COVID protocols. Rugby Canada is making half of the 32,000-capacity lower bowl available and may push that to 60 per cent if demand warrants.